[llvm] [ValueTracking] Compute knownbits from `(icmp upred (add/sub nuw X, Y), C)` (PR #87180)
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Thu Apr 4 18:55:27 PDT 2024
https://github.com/goldsteinn updated https://github.com/llvm/llvm-project/pull/87180
>From 7ab43b6ef7e69d69a5a4d2740aca7121dc9f3bc1 Mon Sep 17 00:00:00 2001
From: Noah Goldstein <goldstein.w.n at gmail.com>
Date: Sat, 30 Mar 2024 21:38:23 -0500
Subject: [PATCH 1/2] [ValueTracking] Add tests for computing knownbits from
`(icmp upred (add/sub nuw X, Y), C)`; NFC
---
.../test/Transforms/InstCombine/known-bits.ll | 225 ++++++++++++++++++
1 file changed, 225 insertions(+)
diff --git a/llvm/test/Transforms/InstCombine/known-bits.ll b/llvm/test/Transforms/InstCombine/known-bits.ll
index 769f7661fc8dc0..d465fa41d039a5 100644
--- a/llvm/test/Transforms/InstCombine/known-bits.ll
+++ b/llvm/test/Transforms/InstCombine/known-bits.ll
@@ -630,5 +630,230 @@ define i8 @or_ne_bits_must_be_unset2_fail(i8 %x, i8 %y) {
ret i8 %r
}
+define i8 @test_icmp_add(i8 %n, i8 %n2, i8 %other) {
+; CHECK-LABEL: @test_icmp_add(
+; CHECK-NEXT: entry:
+; CHECK-NEXT: [[N_ADD:%.*]] = add nuw i8 [[N:%.*]], [[N2:%.*]]
+; CHECK-NEXT: [[CMP:%.*]] = icmp ult i8 [[N_ADD]], 32
+; CHECK-NEXT: br i1 [[CMP]], label [[IF_THEN:%.*]], label [[IF_ELSE:%.*]]
+; CHECK: if.then:
+; CHECK-NEXT: [[R:%.*]] = and i8 [[N]], 32
+; CHECK-NEXT: ret i8 [[R]]
+; CHECK: if.else:
+; CHECK-NEXT: ret i8 [[OTHER:%.*]]
+;
+entry:
+ %n_add = add nuw i8 %n, %n2
+ %cmp = icmp ult i8 %n_add, 32
+ br i1 %cmp, label %if.then, label %if.else
+
+if.then:
+ %r = and i8 %n, 32
+ ret i8 %r
+
+if.else:
+ ret i8 %other
+}
+
+define i8 @test_icmp_add2(i8 %n, i8 %n2, i8 %other) {
+; CHECK-LABEL: @test_icmp_add2(
+; CHECK-NEXT: entry:
+; CHECK-NEXT: [[N_ADD:%.*]] = add nuw i8 [[N:%.*]], [[N2:%.*]]
+; CHECK-NEXT: [[CMP:%.*]] = icmp ugt i8 [[N_ADD]], 14
+; CHECK-NEXT: br i1 [[CMP]], label [[IF_THEN:%.*]], label [[IF_ELSE:%.*]]
+; CHECK: if.then:
+; CHECK-NEXT: ret i8 [[OTHER:%.*]]
+; CHECK: if.else:
+; CHECK-NEXT: [[R:%.*]] = and i8 [[N]], 32
+; CHECK-NEXT: ret i8 [[R]]
+;
+entry:
+ %n_add = add nuw i8 %n, %n2
+ %cmp = icmp uge i8 %n_add, 15
+ br i1 %cmp, label %if.then, label %if.else
+
+if.then:
+ ret i8 %other
+if.else:
+ %r = and i8 %n, 32
+ ret i8 %r
+
+}
+
+define i8 @test_icmp_add_fail_bad_range(i8 %n, i8 %n2, i8 %other) {
+; CHECK-LABEL: @test_icmp_add_fail_bad_range(
+; CHECK-NEXT: entry:
+; CHECK-NEXT: [[N_ADD:%.*]] = add nuw i8 [[N:%.*]], [[N2:%.*]]
+; CHECK-NEXT: [[CMP:%.*]] = icmp ult i8 [[N_ADD]], 33
+; CHECK-NEXT: br i1 [[CMP]], label [[IF_THEN:%.*]], label [[IF_ELSE:%.*]]
+; CHECK: if.then:
+; CHECK-NEXT: [[R:%.*]] = and i8 [[N]], 32
+; CHECK-NEXT: ret i8 [[R]]
+; CHECK: if.else:
+; CHECK-NEXT: ret i8 [[OTHER:%.*]]
+;
+entry:
+ %n_add = add nuw i8 %n, %n2
+ %cmp = icmp ule i8 %n_add, 32
+ br i1 %cmp, label %if.then, label %if.else
+
+if.then:
+ %r = and i8 %n, 32
+ ret i8 %r
+
+if.else:
+ ret i8 %other
+}
+
+define i8 @test_icmp_add_fail_bad_pred(i8 %n, i8 %n2, i8 %other) {
+; CHECK-LABEL: @test_icmp_add_fail_bad_pred(
+; CHECK-NEXT: entry:
+; CHECK-NEXT: [[N_ADD:%.*]] = add nuw i8 [[N:%.*]], [[N2:%.*]]
+; CHECK-NEXT: [[CMP:%.*]] = icmp ugt i8 [[N_ADD]], 32
+; CHECK-NEXT: br i1 [[CMP]], label [[IF_THEN:%.*]], label [[IF_ELSE:%.*]]
+; CHECK: if.then:
+; CHECK-NEXT: [[R:%.*]] = and i8 [[N]], 32
+; CHECK-NEXT: ret i8 [[R]]
+; CHECK: if.else:
+; CHECK-NEXT: ret i8 [[OTHER:%.*]]
+;
+entry:
+ %n_add = add nuw i8 %n, %n2
+ %cmp = icmp ugt i8 %n_add, 32
+ br i1 %cmp, label %if.then, label %if.else
+
+if.then:
+ %r = and i8 %n, 32
+ ret i8 %r
+
+if.else:
+ ret i8 %other
+}
+
+define i8 @test_icmp_sub(i8 %n, i8 %n2, i8 %other) {
+; CHECK-LABEL: @test_icmp_sub(
+; CHECK-NEXT: entry:
+; CHECK-NEXT: [[N_AND:%.*]] = sub nuw i8 [[N:%.*]], [[N2:%.*]]
+; CHECK-NEXT: [[CMP:%.*]] = icmp ugt i8 [[N_AND]], -33
+; CHECK-NEXT: br i1 [[CMP]], label [[IF_THEN:%.*]], label [[IF_ELSE:%.*]]
+; CHECK: if.then:
+; CHECK-NEXT: [[R:%.*]] = and i8 [[N]], 32
+; CHECK-NEXT: ret i8 [[R]]
+; CHECK: if.else:
+; CHECK-NEXT: ret i8 [[OTHER:%.*]]
+;
+entry:
+ %n_sub = sub nuw i8 %n, %n2
+ %cmp = icmp ugt i8 %n_sub, 223
+ br i1 %cmp, label %if.then, label %if.else
+
+if.then:
+ %r = and i8 %n, 32
+ ret i8 %r
+
+if.else:
+ ret i8 %other
+}
+
+define i8 @test_icmp_sub_fail_wrong_arg(i8 %n, i8 %n2, i8 %other) {
+; CHECK-LABEL: @test_icmp_sub_fail_wrong_arg(
+; CHECK-NEXT: entry:
+; CHECK-NEXT: [[N_AND:%.*]] = sub nuw i8 [[N1:%.*]], [[N:%.*]]
+; CHECK-NEXT: [[CMP:%.*]] = icmp ugt i8 [[N_AND]], -33
+; CHECK-NEXT: br i1 [[CMP]], label [[IF_THEN:%.*]], label [[IF_ELSE:%.*]]
+; CHECK: if.then:
+; CHECK-NEXT: [[R:%.*]] = and i8 [[N]], 32
+; CHECK-NEXT: ret i8 [[R]]
+; CHECK: if.else:
+; CHECK-NEXT: ret i8 [[OTHER:%.*]]
+;
+entry:
+ %n_sub = sub nuw i8 %n, %n2
+ %cmp = icmp ugt i8 %n_sub, 223
+ br i1 %cmp, label %if.then, label %if.else
+
+if.then:
+ %r = and i8 %n2, 32
+ ret i8 %r
+
+if.else:
+ ret i8 %other
+}
+
+define i8 @test_icmp_sub2(i8 %n, i8 %n2, i8 %other) {
+; CHECK-LABEL: @test_icmp_sub2(
+; CHECK-NEXT: entry:
+; CHECK-NEXT: [[N_SUB:%.*]] = sub nuw i8 [[N:%.*]], [[N2:%.*]]
+; CHECK-NEXT: [[CMP:%.*]] = icmp ult i8 [[N_SUB]], -31
+; CHECK-NEXT: br i1 [[CMP]], label [[IF_THEN:%.*]], label [[IF_ELSE:%.*]]
+; CHECK: if.then:
+; CHECK-NEXT: ret i8 [[OTHER:%.*]]
+; CHECK: if.else:
+; CHECK-NEXT: [[R:%.*]] = and i8 [[N]], 32
+; CHECK-NEXT: ret i8 [[R]]
+;
+entry:
+ %n_sub = sub nuw i8 %n, %n2
+ %cmp = icmp ule i8 %n_sub, 224
+ br i1 %cmp, label %if.then, label %if.else
+
+if.then:
+ ret i8 %other
+if.else:
+ %r = and i8 %n, 32
+ ret i8 %r
+
+}
+
+define i8 @test_icmp_sub_fail_bad_range(i8 %n, i8 %n2, i8 %other) {
+; CHECK-LABEL: @test_icmp_sub_fail_bad_range(
+; CHECK-NEXT: entry:
+; CHECK-NEXT: [[N_SUB:%.*]] = sub nuw i8 [[N:%.*]], [[N2:%.*]]
+; CHECK-NEXT: [[CMP:%.*]] = icmp ugt i8 [[N_SUB]], -34
+; CHECK-NEXT: br i1 [[CMP]], label [[IF_THEN:%.*]], label [[IF_ELSE:%.*]]
+; CHECK: if.then:
+; CHECK-NEXT: [[R:%.*]] = and i8 [[N]], 32
+; CHECK-NEXT: ret i8 [[R]]
+; CHECK: if.else:
+; CHECK-NEXT: ret i8 [[OTHER:%.*]]
+;
+entry:
+ %n_sub = sub nuw i8 %n, %n2
+ %cmp = icmp uge i8 %n_sub, 223
+ br i1 %cmp, label %if.then, label %if.else
+
+if.then:
+ %r = and i8 %n, 32
+ ret i8 %r
+
+if.else:
+ ret i8 %other
+}
+
+define i8 @test_icmp_sub_fail_bad_pred(i8 %n, i8 %n2, i8 %other) {
+; CHECK-LABEL: @test_icmp_sub_fail_bad_pred(
+; CHECK-NEXT: entry:
+; CHECK-NEXT: [[N_SUB:%.*]] = sub nuw i8 [[N:%.*]], [[N2:%.*]]
+; CHECK-NEXT: [[CMP:%.*]] = icmp sgt i8 [[N_SUB]], 31
+; CHECK-NEXT: br i1 [[CMP]], label [[IF_THEN:%.*]], label [[IF_ELSE:%.*]]
+; CHECK: if.then:
+; CHECK-NEXT: [[R:%.*]] = and i8 [[N]], 32
+; CHECK-NEXT: ret i8 [[R]]
+; CHECK: if.else:
+; CHECK-NEXT: ret i8 [[OTHER:%.*]]
+;
+entry:
+ %n_sub = sub nuw i8 %n, %n2
+ %cmp = icmp sge i8 %n_sub, 32
+ br i1 %cmp, label %if.then, label %if.else
+
+if.then:
+ %r = and i8 %n, 32
+ ret i8 %r
+
+if.else:
+ ret i8 %other
+}
+
declare void @use(i1)
declare void @sink(i8)
>From 6d6bb2970f363e08987eaec492fd7c1e66186471 Mon Sep 17 00:00:00 2001
From: Noah Goldstein <goldstein.w.n at gmail.com>
Date: Sat, 30 Mar 2024 21:39:36 -0500
Subject: [PATCH 2/2] [ValueTracking] Compute knownbits from `(icmp upred
(add/sub nuw X, Y), C)`
`(icmp ule/ult (add nuw X, Y), C)` implies both `(icmp ule/ult X, C)` and
`(icmp ule/ult Y, C)`. We can use this to deduce leading zeros in `X`/`Y`.
`(icmp uge/ugt (sub nuw X, Y), C)` implies `(icmp uge/uge X, C)` . We
can use this to deduce leading ones in `X`.
Proofs: https://alive2.llvm.org/ce/z/sc5k22
---
llvm/lib/Analysis/ValueTracking.cpp | 50 ++++++++++++++-----
.../test/Transforms/InstCombine/known-bits.ll | 12 ++---
2 files changed, 42 insertions(+), 20 deletions(-)
diff --git a/llvm/lib/Analysis/ValueTracking.cpp b/llvm/lib/Analysis/ValueTracking.cpp
index 5ad4da43bca7db..5b4b9acd1f9832 100644
--- a/llvm/lib/Analysis/ValueTracking.cpp
+++ b/llvm/lib/Analysis/ValueTracking.cpp
@@ -701,13 +701,26 @@ static void computeKnownBitsFromCmp(const Value *V, CmpInst::Predicate Pred,
break;
}
default:
- const APInt *Offset = nullptr;
- if (match(LHS, m_CombineOr(m_V, m_AddLike(m_V, m_APInt(Offset)))) &&
- match(RHS, m_APInt(C))) {
- ConstantRange LHSRange = ConstantRange::makeAllowedICmpRegion(Pred, *C);
- if (Offset)
- LHSRange = LHSRange.sub(*Offset);
- Known = Known.unionWith(LHSRange.toKnownBits());
+ if (match(RHS, m_APInt(C))) {
+ const APInt *Offset = nullptr;
+ if (match(LHS, m_CombineOr(m_V, m_AddLike(m_V, m_APInt(Offset))))) {
+ ConstantRange LHSRange = ConstantRange::makeAllowedICmpRegion(Pred, *C);
+ if (Offset)
+ LHSRange = LHSRange.sub(*Offset);
+ Known = Known.unionWith(LHSRange.toKnownBits());
+ }
+ // X nuw+ Y u< C -> X u< C && Y u< C
+ if ((Pred == ICmpInst::ICMP_ULE || Pred == ICmpInst::ICMP_ULT) &&
+ match(LHS, m_c_NUWAdd(m_V, m_Value()))) {
+ Known.Zero.setHighBits(
+ (*C - (Pred == ICmpInst::ICMP_ULT)).countLeadingZeros());
+ }
+ // X nuw- Y u> C -> X u> C
+ if ((Pred == ICmpInst::ICMP_UGE || Pred == ICmpInst::ICMP_UGT) &&
+ match(LHS, m_NUWSub(m_V, m_Value()))) {
+ Known.One.setHighBits(
+ (*C + (Pred == ICmpInst::ICMP_UGT)).countLeadingOnes());
+ }
}
break;
}
@@ -9309,11 +9322,24 @@ void llvm::findValuesAffectedByCondition(
}
}
} else {
- // Handle (A + C1) u< C2, which is the canonical form of
- // A > C3 && A < C4.
- if (match(A, m_AddLike(m_Value(X), m_ConstantInt())) &&
- match(B, m_ConstantInt()))
- AddAffected(X);
+ if (match(B, m_ConstantInt())) {
+ // Handle (A + C1) u< C2, which is the canonical form of
+ // A > C3 && A < C4.
+ if (match(A, m_AddLike(m_Value(X), m_ConstantInt())))
+ AddAffected(X);
+
+ if (ICmpInst::isUnsigned(Pred)) {
+ Value *Y;
+ // X nuw+ Y u< C -> X u< C && Y u< C
+ if (match(A, m_NUWAdd(m_Value(X), m_Value(Y)))) {
+ AddAffected(X);
+ AddAffected(Y);
+ }
+ // X nuw- Y u> C -> X u> C
+ if (match(A, m_NUWSub(m_Value(X), m_Value())))
+ AddAffected(X);
+ }
+ }
// Handle icmp slt/sgt (bitcast X to int), 0/-1, which is supported
// by computeKnownFPClass().
diff --git a/llvm/test/Transforms/InstCombine/known-bits.ll b/llvm/test/Transforms/InstCombine/known-bits.ll
index d465fa41d039a5..ea9eb9b70957c5 100644
--- a/llvm/test/Transforms/InstCombine/known-bits.ll
+++ b/llvm/test/Transforms/InstCombine/known-bits.ll
@@ -637,8 +637,7 @@ define i8 @test_icmp_add(i8 %n, i8 %n2, i8 %other) {
; CHECK-NEXT: [[CMP:%.*]] = icmp ult i8 [[N_ADD]], 32
; CHECK-NEXT: br i1 [[CMP]], label [[IF_THEN:%.*]], label [[IF_ELSE:%.*]]
; CHECK: if.then:
-; CHECK-NEXT: [[R:%.*]] = and i8 [[N]], 32
-; CHECK-NEXT: ret i8 [[R]]
+; CHECK-NEXT: ret i8 0
; CHECK: if.else:
; CHECK-NEXT: ret i8 [[OTHER:%.*]]
;
@@ -664,8 +663,7 @@ define i8 @test_icmp_add2(i8 %n, i8 %n2, i8 %other) {
; CHECK: if.then:
; CHECK-NEXT: ret i8 [[OTHER:%.*]]
; CHECK: if.else:
-; CHECK-NEXT: [[R:%.*]] = and i8 [[N]], 32
-; CHECK-NEXT: ret i8 [[R]]
+; CHECK-NEXT: ret i8 0
;
entry:
%n_add = add nuw i8 %n, %n2
@@ -737,8 +735,7 @@ define i8 @test_icmp_sub(i8 %n, i8 %n2, i8 %other) {
; CHECK-NEXT: [[CMP:%.*]] = icmp ugt i8 [[N_AND]], -33
; CHECK-NEXT: br i1 [[CMP]], label [[IF_THEN:%.*]], label [[IF_ELSE:%.*]]
; CHECK: if.then:
-; CHECK-NEXT: [[R:%.*]] = and i8 [[N]], 32
-; CHECK-NEXT: ret i8 [[R]]
+; CHECK-NEXT: ret i8 32
; CHECK: if.else:
; CHECK-NEXT: ret i8 [[OTHER:%.*]]
;
@@ -789,8 +786,7 @@ define i8 @test_icmp_sub2(i8 %n, i8 %n2, i8 %other) {
; CHECK: if.then:
; CHECK-NEXT: ret i8 [[OTHER:%.*]]
; CHECK: if.else:
-; CHECK-NEXT: [[R:%.*]] = and i8 [[N]], 32
-; CHECK-NEXT: ret i8 [[R]]
+; CHECK-NEXT: ret i8 32
;
entry:
%n_sub = sub nuw i8 %n, %n2
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