[llvm] [InstCombine] Improve coverage of `foldSelectValueEquivalence` (PR #88298)
via llvm-commits
llvm-commits at lists.llvm.org
Thu Jun 6 14:00:34 PDT 2024
https://github.com/goldsteinn updated https://github.com/llvm/llvm-project/pull/88298
>From fe09a0d820fb0fb4c4f27e5a2e96cd2ae42eb4e2 Mon Sep 17 00:00:00 2001
From: Noah Goldstein <goldstein.w.n at gmail.com>
Date: Wed, 10 Apr 2024 12:07:37 -0500
Subject: [PATCH 1/3] [InstCombine] Add tests for expanding
`foldSelectValueEquivalence`; NFC
---
.../InstCombine/select-cmp-eq-op-fold.ll | 186 ++++++++++++++++++
llvm/test/Transforms/InstCombine/select.ll | 46 ++++-
2 files changed, 229 insertions(+), 3 deletions(-)
create mode 100644 llvm/test/Transforms/InstCombine/select-cmp-eq-op-fold.ll
diff --git a/llvm/test/Transforms/InstCombine/select-cmp-eq-op-fold.ll b/llvm/test/Transforms/InstCombine/select-cmp-eq-op-fold.ll
new file mode 100644
index 0000000000000..ec82b1944f723
--- /dev/null
+++ b/llvm/test/Transforms/InstCombine/select-cmp-eq-op-fold.ll
@@ -0,0 +1,186 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; RUN: opt < %s -passes=instcombine -S | FileCheck %s
+
+declare void @use.i1(i1)
+declare void @use.i8(i8)
+define i8 @replace_with_y_noundef(i8 %x, i8 noundef %y, i8 %z) {
+; CHECK-LABEL: @replace_with_y_noundef(
+; CHECK-NEXT: [[CMP:%.*]] = icmp eq i8 [[X:%.*]], [[Y:%.*]]
+; CHECK-NEXT: [[AND:%.*]] = and i8 [[X]], [[Y]]
+; CHECK-NEXT: [[SEL:%.*]] = select i1 [[CMP]], i8 [[AND]], i8 [[Z:%.*]]
+; CHECK-NEXT: ret i8 [[SEL]]
+;
+ %cmp = icmp eq i8 %x, %y
+ %and = and i8 %x, %y
+ %sel = select i1 %cmp, i8 %and, i8 %z
+ ret i8 %sel
+}
+
+define i8 @replace_with_x_noundef(i8 noundef %x, i8 %y, i8 %z) {
+; CHECK-LABEL: @replace_with_x_noundef(
+; CHECK-NEXT: [[CMP:%.*]] = icmp ne i8 [[X:%.*]], [[Y:%.*]]
+; CHECK-NEXT: call void @use.i1(i1 [[CMP]])
+; CHECK-NEXT: [[AND:%.*]] = or i8 [[X]], [[Y]]
+; CHECK-NEXT: [[SEL:%.*]] = select i1 [[CMP]], i8 [[Z:%.*]], i8 [[AND]]
+; CHECK-NEXT: ret i8 [[SEL]]
+;
+ %cmp = icmp ne i8 %x, %y
+ call void @use.i1(i1 %cmp)
+ %and = or i8 %x, %y
+ %sel = select i1 %cmp, i8 %z, i8 %and
+ ret i8 %sel
+}
+
+define i8 @replace_with_x_maybe_undef_fail(i8 %x, i8 %y, i8 %z) {
+; CHECK-LABEL: @replace_with_x_maybe_undef_fail(
+; CHECK-NEXT: [[CMP:%.*]] = icmp ne i8 [[X:%.*]], [[Y:%.*]]
+; CHECK-NEXT: call void @use.i1(i1 [[CMP]])
+; CHECK-NEXT: [[AND:%.*]] = or i8 [[X]], [[Y]]
+; CHECK-NEXT: [[SEL:%.*]] = select i1 [[CMP]], i8 [[Z:%.*]], i8 [[AND]]
+; CHECK-NEXT: ret i8 [[SEL]]
+;
+ %cmp = icmp ne i8 %x, %y
+ call void @use.i1(i1 %cmp)
+ %and = or i8 %x, %y
+ %sel = select i1 %cmp, i8 %z, i8 %and
+ ret i8 %sel
+}
+
+define i8 @replace_with_y_for_new_oneuse(i8 noundef %xx, i8 noundef %y, i8 %z) {
+; CHECK-LABEL: @replace_with_y_for_new_oneuse(
+; CHECK-NEXT: [[X:%.*]] = mul i8 [[XX:%.*]], 13
+; CHECK-NEXT: [[CMP:%.*]] = icmp eq i8 [[X]], [[Y:%.*]]
+; CHECK-NEXT: [[ADD:%.*]] = add nuw i8 [[X]], [[Y]]
+; CHECK-NEXT: [[SEL:%.*]] = select i1 [[CMP]], i8 [[ADD]], i8 [[Z:%.*]]
+; CHECK-NEXT: ret i8 [[SEL]]
+;
+ %x = mul i8 %xx, 13
+ %cmp = icmp eq i8 %x, %y
+ %add = add nuw i8 %x, %y
+ %sel = select i1 %cmp, i8 %add, i8 %z
+ ret i8 %sel
+}
+
+define i8 @replace_with_y_for_new_oneuse2(i8 %xx, i8 noundef %y, i8 %z, i8 %q) {
+; CHECK-LABEL: @replace_with_y_for_new_oneuse2(
+; CHECK-NEXT: [[X:%.*]] = mul i8 [[XX:%.*]], 13
+; CHECK-NEXT: [[CMP:%.*]] = icmp eq i8 [[X]], [[Y:%.*]]
+; CHECK-NEXT: [[ADD:%.*]] = add nuw i8 [[X]], [[Q:%.*]]
+; CHECK-NEXT: [[SEL:%.*]] = select i1 [[CMP]], i8 [[ADD]], i8 [[Z:%.*]]
+; CHECK-NEXT: ret i8 [[SEL]]
+;
+ %x = mul i8 %xx, 13
+ %cmp = icmp eq i8 %x, %y
+ %add = add nuw i8 %x, %q
+ %sel = select i1 %cmp, i8 %add, i8 %z
+ ret i8 %sel
+}
+
+define i8 @replace_with_x_for_new_oneuse(i8 noundef %xx, i8 noundef %yy, i8 %z, i8 %w) {
+; CHECK-LABEL: @replace_with_x_for_new_oneuse(
+; CHECK-NEXT: [[X:%.*]] = mul i8 [[XX:%.*]], 13
+; CHECK-NEXT: [[Y:%.*]] = add i8 [[YY:%.*]], [[W:%.*]]
+; CHECK-NEXT: [[CMP:%.*]] = icmp eq i8 [[X]], [[Y]]
+; CHECK-NEXT: [[MUL:%.*]] = mul i8 [[X]], [[Y]]
+; CHECK-NEXT: [[SEL:%.*]] = select i1 [[CMP]], i8 [[MUL]], i8 [[Z:%.*]]
+; CHECK-NEXT: ret i8 [[SEL]]
+;
+ %x = mul i8 %xx, 13
+ %y = add i8 %yy, %w
+ %cmp = icmp eq i8 %x, %y
+ %mul = mul i8 %x, %y
+ %sel = select i1 %cmp, i8 %mul, i8 %z
+ ret i8 %sel
+}
+
+define i8 @replace_with_x_for_new_oneuse2(i8 noundef %xx, i8 %yy, i8 %z, i8 %w, i8 %q) {
+; CHECK-LABEL: @replace_with_x_for_new_oneuse2(
+; CHECK-NEXT: [[X:%.*]] = mul i8 [[XX:%.*]], 13
+; CHECK-NEXT: [[Y:%.*]] = add i8 [[YY:%.*]], [[W:%.*]]
+; CHECK-NEXT: [[CMP:%.*]] = icmp eq i8 [[X]], [[Y]]
+; CHECK-NEXT: [[MUL:%.*]] = mul i8 [[Y]], [[Q:%.*]]
+; CHECK-NEXT: [[SEL:%.*]] = select i1 [[CMP]], i8 [[MUL]], i8 [[Z:%.*]]
+; CHECK-NEXT: ret i8 [[SEL]]
+;
+ %x = mul i8 %xx, 13
+ %y = add i8 %yy, %w
+ %cmp = icmp eq i8 %x, %y
+ %mul = mul i8 %q, %y
+ %sel = select i1 %cmp, i8 %mul, i8 %z
+ ret i8 %sel
+}
+
+define i8 @replace_with_x_for_simple_binop(i8 noundef %xx, i8 %yy, i8 %z, i8 %w) {
+; CHECK-LABEL: @replace_with_x_for_simple_binop(
+; CHECK-NEXT: [[X:%.*]] = mul i8 [[XX:%.*]], 13
+; CHECK-NEXT: [[Y:%.*]] = add i8 [[YY:%.*]], [[W:%.*]]
+; CHECK-NEXT: [[CMP:%.*]] = icmp eq i8 [[X]], [[Y]]
+; CHECK-NEXT: [[MUL:%.*]] = mul i8 [[X]], [[Y]]
+; CHECK-NEXT: call void @use.i8(i8 [[Y]])
+; CHECK-NEXT: [[SEL:%.*]] = select i1 [[CMP]], i8 [[MUL]], i8 [[Z:%.*]]
+; CHECK-NEXT: ret i8 [[SEL]]
+;
+ %x = mul i8 %xx, 13
+ %y = add i8 %yy, %w
+ %cmp = icmp eq i8 %x, %y
+ %mul = mul i8 %x, %y
+ call void @use.i8(i8 %y)
+ %sel = select i1 %cmp, i8 %mul, i8 %z
+ ret i8 %sel
+}
+
+define i8 @replace_with_none_for_new_oneuse_fail_maybe_undef(i8 %xx, i8 %y, i8 %z) {
+; CHECK-LABEL: @replace_with_none_for_new_oneuse_fail_maybe_undef(
+; CHECK-NEXT: [[X:%.*]] = mul i8 [[XX:%.*]], 13
+; CHECK-NEXT: [[CMP:%.*]] = icmp eq i8 [[X]], [[Y:%.*]]
+; CHECK-NEXT: [[MUL:%.*]] = mul i8 [[X]], [[Y]]
+; CHECK-NEXT: [[SEL:%.*]] = select i1 [[CMP]], i8 [[MUL]], i8 [[Z:%.*]]
+; CHECK-NEXT: ret i8 [[SEL]]
+;
+ %x = mul i8 %xx, 13
+ %cmp = icmp eq i8 %x, %y
+ %mul = mul i8 %x, %y
+ %sel = select i1 %cmp, i8 %mul, i8 %z
+ ret i8 %sel
+}
+
+define i8 @replace_with_y_for_simple_binop(i8 %x, i8 noundef %y, i8 %z) {
+; CHECK-LABEL: @replace_with_y_for_simple_binop(
+; CHECK-NEXT: [[CMP:%.*]] = icmp eq i8 [[X:%.*]], [[Y:%.*]]
+; CHECK-NEXT: [[MUL:%.*]] = mul nsw i8 [[X]], [[Y]]
+; CHECK-NEXT: [[SEL:%.*]] = select i1 [[CMP]], i8 [[MUL]], i8 [[Z:%.*]]
+; CHECK-NEXT: ret i8 [[SEL]]
+;
+ %cmp = icmp eq i8 %x, %y
+ %mul = mul nsw i8 %x, %y
+ %sel = select i1 %cmp, i8 %mul, i8 %z
+ ret i8 %sel
+}
+
+define i8 @replace_with_y_for_simple_binop_fail_multiuse(i8 %x, i8 noundef %y, i8 %z) {
+; CHECK-LABEL: @replace_with_y_for_simple_binop_fail_multiuse(
+; CHECK-NEXT: [[CMP:%.*]] = icmp eq i8 [[X:%.*]], [[Y:%.*]]
+; CHECK-NEXT: [[MUL:%.*]] = mul nsw i8 [[X]], [[Y]]
+; CHECK-NEXT: [[SEL:%.*]] = select i1 [[CMP]], i8 [[MUL]], i8 [[Z:%.*]]
+; CHECK-NEXT: call void @use.i8(i8 [[MUL]])
+; CHECK-NEXT: ret i8 [[SEL]]
+;
+ %cmp = icmp eq i8 %x, %y
+ %mul = mul nsw i8 %x, %y
+ %sel = select i1 %cmp, i8 %mul, i8 %z
+ call void @use.i8(i8 %mul)
+ ret i8 %sel
+}
+
+define i8 @replace_with_y_for_simple_binop_fail(i8 %x, i8 noundef %y, i8 %z, i8 %q) {
+; CHECK-LABEL: @replace_with_y_for_simple_binop_fail(
+; CHECK-NEXT: [[CMP:%.*]] = icmp eq i8 [[X:%.*]], [[Y:%.*]]
+; CHECK-NEXT: [[MUL:%.*]] = mul nsw i8 [[X]], [[Q:%.*]]
+; CHECK-NEXT: [[SEL:%.*]] = select i1 [[CMP]], i8 [[MUL]], i8 [[Z:%.*]]
+; CHECK-NEXT: ret i8 [[SEL]]
+;
+ %cmp = icmp eq i8 %x, %y
+ %mul = mul nsw i8 %x, %q
+ %sel = select i1 %cmp, i8 %mul, i8 %z
+ ret i8 %sel
+}
diff --git a/llvm/test/Transforms/InstCombine/select.ll b/llvm/test/Transforms/InstCombine/select.ll
index a0ee4383495cc..5cc4ee360db9f 100644
--- a/llvm/test/Transforms/InstCombine/select.ll
+++ b/llvm/test/Transforms/InstCombine/select.ll
@@ -667,7 +667,7 @@ define i1 @test39(i1 %cond, double %x) {
; CHECK-LABEL: @test39(
; CHECK-NEXT: ret i1 true
;
- %s = select i1 %cond, double %x, double 0x7FF0000000000000 ; RHS = +infty
+ %s = select i1 %cond, double %x, double 0x7FF0000000000000 ; RHS = +infty
%cmp = fcmp ule double %x, %s
ret i1 %cmp
}
@@ -1364,7 +1364,7 @@ define i32 @PR23757_ne(i32 %x, ptr %p) {
; CHECK-NEXT: ret i32 -2147483648
;
%cmp = icmp ne i32 %x, 2147483647
- store i1 %cmp, ptr %p ; thwart predicate canonicalization
+ store i1 %cmp, ptr %p ; thwart predicate canonicalization
%add = add nsw i32 %x, 1
%sel = select i1 %cmp, i32 -2147483648, i32 %add
ret i32 %sel
@@ -1378,7 +1378,7 @@ define i32 @PR23757_ne_swapped(i32 %x, ptr %p) {
; CHECK-NEXT: ret i32 [[ADD]]
;
%cmp = icmp ne i32 %x, 2147483647
- store i1 %cmp, ptr %p ; thwart predicate canonicalization
+ store i1 %cmp, ptr %p ; thwart predicate canonicalization
%add = add nsw i32 %x, 1
%sel = select i1 %cmp, i32 %add, i32 -2147483648
ret i32 %sel
@@ -2809,6 +2809,46 @@ define <2 x i8> @select_replacement_add_eq_vec_undef(<2 x i8> %x, <2 x i8> %y) {
ret <2 x i8> %sel
}
+define <2 x i8> @select_replacement_add_eq_vec_undef_okay(<2 x i8> %x, <2 x i8> %y) {
+; CHECK-LABEL: @select_replacement_add_eq_vec_undef_okay(
+; CHECK-NEXT: [[CMP:%.*]] = icmp eq <2 x i8> [[X:%.*]], <i8 1, i8 1>
+; CHECK-NEXT: [[SEL:%.*]] = select <2 x i1> [[CMP]], <2 x i8> <i8 2, i8 undef>, <2 x i8> [[Y:%.*]]
+; CHECK-NEXT: ret <2 x i8> [[SEL]]
+;
+ %cmp = icmp eq <2 x i8> %x, <i8 1, i8 1>
+ %add = add <2 x i8> %x, <i8 1, i8 undef>
+ %sel = select <2 x i1> %cmp, <2 x i8> %add, <2 x i8> %y
+ ret <2 x i8> %sel
+}
+
+
+define <2 x i8> @select_replacement_add_eq_vec_undef_okay_todo(<2 x i8> %x, <2 x i8> %y) {
+; CHECK-LABEL: @select_replacement_add_eq_vec_undef_okay_todo(
+; CHECK-NEXT: [[CMP:%.*]] = icmp eq <2 x i8> [[X:%.*]], <i8 1, i8 undef>
+; CHECK-NEXT: [[ADD:%.*]] = add <2 x i8> [[X]], <i8 1, i8 undef>
+; CHECK-NEXT: [[SEL:%.*]] = select <2 x i1> [[CMP]], <2 x i8> [[ADD]], <2 x i8> [[Y:%.*]]
+; CHECK-NEXT: ret <2 x i8> [[SEL]]
+;
+ %cmp = icmp eq <2 x i8> %x, <i8 1, i8 undef>
+ %add = add <2 x i8> %x, <i8 1, i8 undef>
+ %sel = select <2 x i1> %cmp, <2 x i8> %add, <2 x i8> %y
+ ret <2 x i8> %sel
+}
+
+define <2 x i8> @select_replacement_xor_eq_vec(<2 x i8> %x, <2 x i8> %y, <2 x i8> %z) {
+; CHECK-LABEL: @select_replacement_xor_eq_vec(
+; CHECK-NEXT: [[CMP:%.*]] = icmp eq <2 x i8> [[X:%.*]], [[Y:%.*]]
+; CHECK-NEXT: [[ADD:%.*]] = xor <2 x i8> [[X]], [[Y]]
+; CHECK-NEXT: [[SEL:%.*]] = select <2 x i1> [[CMP]], <2 x i8> [[ADD]], <2 x i8> [[Z:%.*]]
+; CHECK-NEXT: ret <2 x i8> [[SEL]]
+;
+ %cmp = icmp eq <2 x i8> %x, %y
+ %add = xor <2 x i8> %x, %y
+ %sel = select <2 x i1> %cmp, <2 x i8> %add, <2 x i8> %z
+ ret <2 x i8> %sel
+}
+
+
define i8 @select_replacement_add_ne(i8 %x, i8 %y) {
; CHECK-LABEL: @select_replacement_add_ne(
; CHECK-NEXT: [[CMP:%.*]] = icmp ne i8 [[X:%.*]], 1
>From c727c1b95fda38bac700ab2113ec7362e5ea1a62 Mon Sep 17 00:00:00 2001
From: Noah Goldstein <goldstein.w.n at gmail.com>
Date: Wed, 5 Jun 2024 11:30:53 -0500
Subject: [PATCH 2/3] [InstCombine] Improve coverage of
`foldSelectValueEquivalence` for constants
We don't need the `noundef` check if the new simplification is a
constant.
This cleans up regressions from folding multiuse:
`(icmp eq/ne (sub/xor x, y), 0)` -> `(icmp eq/ne x, y)`.
---
.../InstCombine/InstCombineSelect.cpp | 59 ++++++++++++-------
llvm/test/Transforms/InstCombine/abs-1.ll | 7 +--
llvm/test/Transforms/InstCombine/select.ll | 6 +-
3 files changed, 42 insertions(+), 30 deletions(-)
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp b/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
index d2aaa5e230545..77162ca9f6a1d 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
@@ -1288,20 +1288,36 @@ Instruction *InstCombinerImpl::foldSelectValueEquivalence(SelectInst &Sel,
Swapped = true;
}
- // In X == Y ? f(X) : Z, try to evaluate f(Y) and replace the operand.
- // Make sure Y cannot be undef though, as we might pick different values for
- // undef in the icmp and in f(Y). Additionally, take care to avoid replacing
- // X == Y ? X : Z with X == Y ? Y : Z, as that would lead to an infinite
- // replacement cycle.
Value *CmpLHS = Cmp.getOperand(0), *CmpRHS = Cmp.getOperand(1);
- if (TrueVal != CmpLHS && isGuaranteedNotToBeUndef(CmpRHS, SQ.AC, &Sel, &DT)) {
- if (Value *V = simplifyWithOpReplaced(TrueVal, CmpLHS, CmpRHS, SQ,
- /* AllowRefinement */ true))
- // Require either the replacement or the simplification result to be a
- // constant to avoid infinite loops.
- // FIXME: Make this check more precise.
- if (isa<Constant>(CmpRHS) || isa<Constant>(V))
+ auto ReplaceOldOpWithNewOp = [&](Value *OldOp,
+ Value *NewOp) -> Instruction * {
+ // In X == Y ? f(X) : Z, try to evaluate f(Y) and replace the operand.
+ // Take care to avoid replacing X == Y ? X : Z with X == Y ? Y : Z, as that
+ // would lead to an infinite replacement cycle.
+ // If we will be able to evaluate f(Y) to a constant, we can allow undef,
+ // otherwise Y cannot be undef as we might pick different values for undef
+ // in the icmp and in f(Y).
+ if (TrueVal == OldOp)
+ return nullptr;
+
+ if (Value *V = simplifyWithOpReplaced(TrueVal, OldOp, NewOp, SQ,
+ /* AllowRefinement=*/true)) {
+ // Need some guarantees about the new simplified op to ensure we don't inf
+ // loop.
+ // If we simplify to a constant, replace if we aren't creating new undef.
+ if (match(V, m_ImmConstant())) {
+ if (isGuaranteedNotToBeUndef(V, SQ.AC, &Sel, &DT) ||
+ isGuaranteedNotToBeUndef(NewOp, SQ.AC, &Sel, &DT))
+ return replaceOperand(Sel, Swapped ? 2 : 1, V);
+ return nullptr;
+ }
+
+ // If NewOp is a constant and OldOp is not replace iff NewOp doesn't
+ // contain and undef elements.
+ if (match(NewOp, m_ImmConstant()) &&
+ isGuaranteedNotToBeUndef(NewOp, SQ.AC, &Sel, &DT))
return replaceOperand(Sel, Swapped ? 2 : 1, V);
+ }
// Even if TrueVal does not simplify, we can directly replace a use of
// CmpLHS with CmpRHS, as long as the instruction is not used anywhere
@@ -1310,16 +1326,17 @@ Instruction *InstCombinerImpl::foldSelectValueEquivalence(SelectInst &Sel,
// undefined behavior). Only do this if CmpRHS is a constant, as
// profitability is not clear for other cases.
// FIXME: Support vectors.
- if (match(CmpRHS, m_ImmConstant()) && !match(CmpLHS, m_ImmConstant()) &&
- !Cmp.getType()->isVectorTy())
- if (replaceInInstruction(TrueVal, CmpLHS, CmpRHS))
+ if (OldOp == CmpLHS && match(NewOp, m_ImmConstant()) &&
+ !match(OldOp, m_ImmConstant()) && !Cmp.getType()->isVectorTy())
+ if (replaceInInstruction(TrueVal, OldOp, NewOp))
return &Sel;
- }
- if (TrueVal != CmpRHS && isGuaranteedNotToBeUndef(CmpLHS, SQ.AC, &Sel, &DT))
- if (Value *V = simplifyWithOpReplaced(TrueVal, CmpRHS, CmpLHS, SQ,
- /* AllowRefinement */ true))
- if (isa<Constant>(CmpLHS) || isa<Constant>(V))
- return replaceOperand(Sel, Swapped ? 2 : 1, V);
+ return nullptr;
+ };
+
+ if (Instruction *R = ReplaceOldOpWithNewOp(CmpLHS, CmpRHS))
+ return R;
+ if (Instruction *R = ReplaceOldOpWithNewOp(CmpRHS, CmpLHS))
+ return R;
auto *FalseInst = dyn_cast<Instruction>(FalseVal);
if (!FalseInst)
diff --git a/llvm/test/Transforms/InstCombine/abs-1.ll b/llvm/test/Transforms/InstCombine/abs-1.ll
index 32bd7a37053ed..0cf7cd97d8ff4 100644
--- a/llvm/test/Transforms/InstCombine/abs-1.ll
+++ b/llvm/test/Transforms/InstCombine/abs-1.ll
@@ -852,11 +852,8 @@ define i8 @abs_diff_signed_sgt_nuw_extra_use3(i8 %a, i8 %b) {
define i32 @abs_diff_signed_slt_swap_wrong_pred1(i32 %a, i32 %b) {
; CHECK-LABEL: @abs_diff_signed_slt_swap_wrong_pred1(
-; CHECK-NEXT: [[CMP:%.*]] = icmp eq i32 [[A:%.*]], [[B:%.*]]
-; CHECK-NEXT: [[SUB_BA:%.*]] = sub nsw i32 [[B]], [[A]]
-; CHECK-NEXT: [[SUB_AB:%.*]] = sub nsw i32 [[A]], [[B]]
-; CHECK-NEXT: [[COND:%.*]] = select i1 [[CMP]], i32 [[SUB_BA]], i32 [[SUB_AB]]
-; CHECK-NEXT: ret i32 [[COND]]
+; CHECK-NEXT: [[SUB_AB:%.*]] = sub nsw i32 [[A:%.*]], [[B:%.*]]
+; CHECK-NEXT: ret i32 [[SUB_AB]]
;
%cmp = icmp eq i32 %a, %b
%sub_ba = sub nsw i32 %b, %a
diff --git a/llvm/test/Transforms/InstCombine/select.ll b/llvm/test/Transforms/InstCombine/select.ll
index 5cc4ee360db9f..846ede45028e2 100644
--- a/llvm/test/Transforms/InstCombine/select.ll
+++ b/llvm/test/Transforms/InstCombine/select.ll
@@ -2838,8 +2838,7 @@ define <2 x i8> @select_replacement_add_eq_vec_undef_okay_todo(<2 x i8> %x, <2 x
define <2 x i8> @select_replacement_xor_eq_vec(<2 x i8> %x, <2 x i8> %y, <2 x i8> %z) {
; CHECK-LABEL: @select_replacement_xor_eq_vec(
; CHECK-NEXT: [[CMP:%.*]] = icmp eq <2 x i8> [[X:%.*]], [[Y:%.*]]
-; CHECK-NEXT: [[ADD:%.*]] = xor <2 x i8> [[X]], [[Y]]
-; CHECK-NEXT: [[SEL:%.*]] = select <2 x i1> [[CMP]], <2 x i8> [[ADD]], <2 x i8> [[Z:%.*]]
+; CHECK-NEXT: [[SEL:%.*]] = select <2 x i1> [[CMP]], <2 x i8> zeroinitializer, <2 x i8> [[Z:%.*]]
; CHECK-NEXT: ret <2 x i8> [[SEL]]
;
%cmp = icmp eq <2 x i8> %x, %y
@@ -2905,8 +2904,7 @@ define i8 @select_replacement_sub_noundef_but_may_be_poison(i8 %x, i8 noundef %y
define i8 @select_replacement_sub(i8 %x, i8 %y, i8 %z) {
; CHECK-LABEL: @select_replacement_sub(
; CHECK-NEXT: [[CMP:%.*]] = icmp eq i8 [[X:%.*]], [[Y:%.*]]
-; CHECK-NEXT: [[SUB:%.*]] = sub i8 [[X]], [[Y]]
-; CHECK-NEXT: [[SEL:%.*]] = select i1 [[CMP]], i8 [[SUB]], i8 [[Z:%.*]]
+; CHECK-NEXT: [[SEL:%.*]] = select i1 [[CMP]], i8 0, i8 [[Z:%.*]]
; CHECK-NEXT: ret i8 [[SEL]]
;
%cmp = icmp eq i8 %x, %y
>From 750b54f714406cf3a04cd31463afe6e1ff899fdf Mon Sep 17 00:00:00 2001
From: Noah Goldstein <goldstein.w.n at gmail.com>
Date: Wed, 5 Jun 2024 11:35:13 -0500
Subject: [PATCH 3/3] [InstCombine] Improve coverage of
`foldSelectValueEquivalence` for non-constants
There are a few more cases we can easily cover.
- If f(Y) simplifies to Y
- If replace X with Y makes X one-use (and make Y non one-use).
These all require that Y is not undef or poison
---
.../InstCombine/InstCombineSelect.cpp | 51 +++++++++++++++++--
.../InstCombine/select-cmp-eq-op-fold.ll | 16 +++---
2 files changed, 54 insertions(+), 13 deletions(-)
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp b/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
index 77162ca9f6a1d..f61bbdf6b5141 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
@@ -1300,6 +1300,8 @@ Instruction *InstCombinerImpl::foldSelectValueEquivalence(SelectInst &Sel,
if (TrueVal == OldOp)
return nullptr;
+ bool NewOpNeverUndef = false;
+
if (Value *V = simplifyWithOpReplaced(TrueVal, OldOp, NewOp, SQ,
/* AllowRefinement=*/true)) {
// Need some guarantees about the new simplified op to ensure we don't inf
@@ -1312,11 +1314,52 @@ Instruction *InstCombinerImpl::foldSelectValueEquivalence(SelectInst &Sel,
return nullptr;
}
- // If NewOp is a constant and OldOp is not replace iff NewOp doesn't
- // contain and undef elements.
- if (match(NewOp, m_ImmConstant()) &&
- isGuaranteedNotToBeUndef(NewOp, SQ.AC, &Sel, &DT))
+ // We can't do any further replacement if NewOp may be undef/poison.
+ if (!isGuaranteedNotToBeUndefOrPoison(NewOp, SQ.AC, &Sel, &DT))
+ return nullptr;
+
+ // If NewOp is a constant, replace.
+ if (match(NewOp, m_ImmConstant()))
+ return replaceOperand(Sel, Swapped ? 2 : 1, V);
+
+ // If we simplified the TrueArm -> NewOp then replace.
+ // This handles things like `select`/`min`/`max`/`or`/`and`/etc...
+ if (NewOp == V)
return replaceOperand(Sel, Swapped ? 2 : 1, V);
+
+ NewOpNeverUndef = true;
+ }
+
+ // If we can't simplify, but we will either:
+ // 1) Create a new binop where both ops are NewOp i.e (add x, y) is "worse"
+ // than (add y, y) in this case, wait until the second call so we don't
+ // miss a one-use simplification.
+ // 2) Create a new one-use instruction.
+ // proceed.
+ if (TrueVal->hasOneUse() && isa<Instruction>(TrueVal)) {
+ bool BinOpMatch =
+ match(TrueVal, m_c_BinOp(m_Specific(OldOp), m_Specific(NewOp)));
+ bool NewOneUse = isa<Instruction>(OldOp) && OldOp->hasNUses(2) &&
+ (!isa<Instruction>(NewOp) || !NewOp->hasOneUse());
+ if (BinOpMatch || NewOneUse) {
+ bool Replaced = false;
+ auto *TrueIns = cast<Instruction>(TrueVal);
+ for (unsigned OpIdx = 0; OpIdx < TrueIns->getNumOperands(); ++OpIdx) {
+ if (TrueIns->getOperand(OpIdx) != OldOp)
+ continue;
+ // Need to ensure NewOp is noundef (same reason as above). Wait
+ // until the last moment to do this check as it can be relatively
+ // expensive.
+ if (!NewOpNeverUndef &&
+ !isGuaranteedNotToBeUndefOrPoison(NewOp, SQ.AC, &Sel, &DT))
+ break;
+ NewOpNeverUndef = true;
+ TrueIns->setOperand(OpIdx, NewOp);
+ Replaced = true;
+ }
+ if (Replaced)
+ return replaceOperand(Sel, Swapped ? 2 : 1, TrueIns);
+ }
}
// Even if TrueVal does not simplify, we can directly replace a use of
diff --git a/llvm/test/Transforms/InstCombine/select-cmp-eq-op-fold.ll b/llvm/test/Transforms/InstCombine/select-cmp-eq-op-fold.ll
index ec82b1944f723..d2a5c71025370 100644
--- a/llvm/test/Transforms/InstCombine/select-cmp-eq-op-fold.ll
+++ b/llvm/test/Transforms/InstCombine/select-cmp-eq-op-fold.ll
@@ -6,8 +6,7 @@ declare void @use.i8(i8)
define i8 @replace_with_y_noundef(i8 %x, i8 noundef %y, i8 %z) {
; CHECK-LABEL: @replace_with_y_noundef(
; CHECK-NEXT: [[CMP:%.*]] = icmp eq i8 [[X:%.*]], [[Y:%.*]]
-; CHECK-NEXT: [[AND:%.*]] = and i8 [[X]], [[Y]]
-; CHECK-NEXT: [[SEL:%.*]] = select i1 [[CMP]], i8 [[AND]], i8 [[Z:%.*]]
+; CHECK-NEXT: [[SEL:%.*]] = select i1 [[CMP]], i8 [[Y]], i8 [[Z:%.*]]
; CHECK-NEXT: ret i8 [[SEL]]
;
%cmp = icmp eq i8 %x, %y
@@ -20,8 +19,7 @@ define i8 @replace_with_x_noundef(i8 noundef %x, i8 %y, i8 %z) {
; CHECK-LABEL: @replace_with_x_noundef(
; CHECK-NEXT: [[CMP:%.*]] = icmp ne i8 [[X:%.*]], [[Y:%.*]]
; CHECK-NEXT: call void @use.i1(i1 [[CMP]])
-; CHECK-NEXT: [[AND:%.*]] = or i8 [[X]], [[Y]]
-; CHECK-NEXT: [[SEL:%.*]] = select i1 [[CMP]], i8 [[Z:%.*]], i8 [[AND]]
+; CHECK-NEXT: [[SEL:%.*]] = select i1 [[CMP]], i8 [[Z:%.*]], i8 [[X]]
; CHECK-NEXT: ret i8 [[SEL]]
;
%cmp = icmp ne i8 %x, %y
@@ -50,7 +48,7 @@ define i8 @replace_with_y_for_new_oneuse(i8 noundef %xx, i8 noundef %y, i8 %z) {
; CHECK-LABEL: @replace_with_y_for_new_oneuse(
; CHECK-NEXT: [[X:%.*]] = mul i8 [[XX:%.*]], 13
; CHECK-NEXT: [[CMP:%.*]] = icmp eq i8 [[X]], [[Y:%.*]]
-; CHECK-NEXT: [[ADD:%.*]] = add nuw i8 [[X]], [[Y]]
+; CHECK-NEXT: [[ADD:%.*]] = shl nuw i8 [[Y]], 1
; CHECK-NEXT: [[SEL:%.*]] = select i1 [[CMP]], i8 [[ADD]], i8 [[Z:%.*]]
; CHECK-NEXT: ret i8 [[SEL]]
;
@@ -65,7 +63,7 @@ define i8 @replace_with_y_for_new_oneuse2(i8 %xx, i8 noundef %y, i8 %z, i8 %q) {
; CHECK-LABEL: @replace_with_y_for_new_oneuse2(
; CHECK-NEXT: [[X:%.*]] = mul i8 [[XX:%.*]], 13
; CHECK-NEXT: [[CMP:%.*]] = icmp eq i8 [[X]], [[Y:%.*]]
-; CHECK-NEXT: [[ADD:%.*]] = add nuw i8 [[X]], [[Q:%.*]]
+; CHECK-NEXT: [[ADD:%.*]] = add nuw i8 [[Y]], [[Q:%.*]]
; CHECK-NEXT: [[SEL:%.*]] = select i1 [[CMP]], i8 [[ADD]], i8 [[Z:%.*]]
; CHECK-NEXT: ret i8 [[SEL]]
;
@@ -81,7 +79,7 @@ define i8 @replace_with_x_for_new_oneuse(i8 noundef %xx, i8 noundef %yy, i8 %z,
; CHECK-NEXT: [[X:%.*]] = mul i8 [[XX:%.*]], 13
; CHECK-NEXT: [[Y:%.*]] = add i8 [[YY:%.*]], [[W:%.*]]
; CHECK-NEXT: [[CMP:%.*]] = icmp eq i8 [[X]], [[Y]]
-; CHECK-NEXT: [[MUL:%.*]] = mul i8 [[X]], [[Y]]
+; CHECK-NEXT: [[MUL:%.*]] = mul i8 [[X]], [[X]]
; CHECK-NEXT: [[SEL:%.*]] = select i1 [[CMP]], i8 [[MUL]], i8 [[Z:%.*]]
; CHECK-NEXT: ret i8 [[SEL]]
;
@@ -115,7 +113,7 @@ define i8 @replace_with_x_for_simple_binop(i8 noundef %xx, i8 %yy, i8 %z, i8 %w)
; CHECK-NEXT: [[X:%.*]] = mul i8 [[XX:%.*]], 13
; CHECK-NEXT: [[Y:%.*]] = add i8 [[YY:%.*]], [[W:%.*]]
; CHECK-NEXT: [[CMP:%.*]] = icmp eq i8 [[X]], [[Y]]
-; CHECK-NEXT: [[MUL:%.*]] = mul i8 [[X]], [[Y]]
+; CHECK-NEXT: [[MUL:%.*]] = mul i8 [[X]], [[X]]
; CHECK-NEXT: call void @use.i8(i8 [[Y]])
; CHECK-NEXT: [[SEL:%.*]] = select i1 [[CMP]], i8 [[MUL]], i8 [[Z:%.*]]
; CHECK-NEXT: ret i8 [[SEL]]
@@ -147,7 +145,7 @@ define i8 @replace_with_none_for_new_oneuse_fail_maybe_undef(i8 %xx, i8 %y, i8 %
define i8 @replace_with_y_for_simple_binop(i8 %x, i8 noundef %y, i8 %z) {
; CHECK-LABEL: @replace_with_y_for_simple_binop(
; CHECK-NEXT: [[CMP:%.*]] = icmp eq i8 [[X:%.*]], [[Y:%.*]]
-; CHECK-NEXT: [[MUL:%.*]] = mul nsw i8 [[X]], [[Y]]
+; CHECK-NEXT: [[MUL:%.*]] = mul nsw i8 [[Y]], [[Y]]
; CHECK-NEXT: [[SEL:%.*]] = select i1 [[CMP]], i8 [[MUL]], i8 [[Z:%.*]]
; CHECK-NEXT: ret i8 [[SEL]]
;
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