[llvm] [InstCombine] Fold icmp of trunc nuw/nsw (PR #90436)
Nikita Popov via llvm-commits
llvm-commits at lists.llvm.org
Mon Apr 29 00:54:09 PDT 2024
https://github.com/nikic created https://github.com/llvm/llvm-project/pull/90436
Convert the existing foldICmpTruncWithTruncOrExt() fold to work with trunc nowrap flags instead of computeKnownBits(). This also allows us to generalize the fold to work with signed comparisons.
Interestingly, apart from the obvious combinations like signed predicates with trunc nsw, some non-obvious ones are also legal. For example for unsigned predicates we can do the transform for two trunc nsw as well (rather than only trunc nuw).
Proofs: https://alive2.llvm.org/ce/z/ndewwK
>From 36d5822b85aab09e9b525f80713cacb863ee7a75 Mon Sep 17 00:00:00 2001
From: Nikita Popov <npopov at redhat.com>
Date: Mon, 29 Apr 2024 15:32:17 +0900
Subject: [PATCH] [InstCombine] Fold icmp of trunc nuw/nsw
Convert the existing foldICmpTruncWithTruncOrExt() fold to work
with trunc nowrap flags instead of computeKnownBits(). This also
allows us to generalize the fold to work with signed comparisons.
Interesting, apart from the obvious combinations like signed
predicates with trunc nsw, some non-obvious ones are also legal.
For example for unsigned predicated we can do the transform for
two trunc nsw as well (rather than only trunc nuw).
Proofs: https://alive2.llvm.org/ce/z/ndewwK
---
llvm/include/llvm/IR/PatternMatch.h | 27 +++++++
.../InstCombine/InstCombineCompares.cpp | 55 +++++++------
.../InstCombine/icmp-of-trunc-ext.ll | 77 +++++++------------
3 files changed, 83 insertions(+), 76 deletions(-)
diff --git a/llvm/include/llvm/IR/PatternMatch.h b/llvm/include/llvm/IR/PatternMatch.h
index 0b13b4aad9c326..f063e6531dda4f 100644
--- a/llvm/include/llvm/IR/PatternMatch.h
+++ b/llvm/include/llvm/IR/PatternMatch.h
@@ -1839,6 +1839,19 @@ template <typename Op_t> struct NNegZExt_match {
}
};
+template <typename Op_t, unsigned WrapFlags = 0> struct NoWrapTrunc_match {
+ Op_t Op;
+
+ NoWrapTrunc_match(const Op_t &OpMatch) : Op(OpMatch) {}
+
+ template <typename OpTy> bool match(OpTy *V) {
+ if (auto *I = dyn_cast<TruncInst>(V))
+ return (I->getNoWrapKind() & WrapFlags) == WrapFlags &&
+ Op.match(I->getOperand(0));
+ return false;
+ }
+};
+
/// Matches BitCast.
template <typename OpTy>
inline CastOperator_match<OpTy, Instruction::BitCast>
@@ -1900,6 +1913,20 @@ inline CastOperator_match<OpTy, Instruction::Trunc> m_Trunc(const OpTy &Op) {
return CastOperator_match<OpTy, Instruction::Trunc>(Op);
}
+/// Matches trunc nuw.
+template <typename OpTy>
+inline NoWrapTrunc_match<OpTy, TruncInst::NoUnsignedWrap>
+m_NUWTrunc(const OpTy &Op) {
+ return NoWrapTrunc_match<OpTy, TruncInst::NoUnsignedWrap>(Op);
+}
+
+/// Matches trunc nsw.
+template <typename OpTy>
+inline NoWrapTrunc_match<OpTy, TruncInst::NoSignedWrap>
+m_NSWTrunc(const OpTy &Op) {
+ return NoWrapTrunc_match<OpTy, TruncInst::NoSignedWrap>(Op);
+}
+
template <typename OpTy>
inline match_combine_or<CastOperator_match<OpTy, Instruction::Trunc>, OpTy>
m_TruncOrSelf(const OpTy &Op) {
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp b/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
index 1064340cb53661..317b3aef40a97c 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
@@ -1479,19 +1479,29 @@ Instruction *InstCombinerImpl::foldICmpTruncConstant(ICmpInst &Cmp,
return nullptr;
}
-/// Fold icmp (trunc X), (trunc Y).
-/// Fold icmp (trunc X), (zext Y).
+/// Fold icmp (trunc nuw/nsw X), (trunc nuw/nsw Y).
+/// Fold icmp (trunc nuw/nsw X), (zext/sext Y).
Instruction *
InstCombinerImpl::foldICmpTruncWithTruncOrExt(ICmpInst &Cmp,
const SimplifyQuery &Q) {
- if (Cmp.isSigned())
- return nullptr;
-
Value *X, *Y;
ICmpInst::Predicate Pred;
- bool YIsZext = false;
+ bool YIsSExt = false;
// Try to match icmp (trunc X), (trunc Y)
if (match(&Cmp, m_ICmp(Pred, m_Trunc(m_Value(X)), m_Trunc(m_Value(Y))))) {
+ unsigned NoWrapFlags = cast<TruncInst>(Cmp.getOperand(0))->getNoWrapKind() &
+ cast<TruncInst>(Cmp.getOperand(1))->getNoWrapKind();
+ if (Cmp.isSigned()) {
+ // For signed comparisons, both truncs must be nsw.
+ if (!(NoWrapFlags & TruncInst::NoSignedWrap))
+ return nullptr;
+ } else {
+ // For unsigned and equality comparisons, either both must be nuw or
+ // both must be nsw, we don't care which.
+ if (!NoWrapFlags)
+ return nullptr;
+ }
+
if (X->getType() != Y->getType() &&
(!Cmp.getOperand(0)->hasOneUse() || !Cmp.getOperand(1)->hasOneUse()))
return nullptr;
@@ -1501,12 +1511,19 @@ InstCombinerImpl::foldICmpTruncWithTruncOrExt(ICmpInst &Cmp,
Pred = Cmp.getSwappedPredicate(Pred);
}
}
- // Try to match icmp (trunc X), (zext Y)
- else if (match(&Cmp, m_c_ICmp(Pred, m_Trunc(m_Value(X)),
- m_OneUse(m_ZExt(m_Value(Y))))))
-
- YIsZext = true;
- else
+ // Try to match icmp (trunc nuw X), (zext Y)
+ else if (!Cmp.isSigned() &&
+ match(&Cmp, m_c_ICmp(Pred, m_NUWTrunc(m_Value(X)),
+ m_OneUse(m_ZExt(m_Value(Y)))))) {
+ // Can fold trunc nuw + zext for unsigned and equality predicates.
+ }
+ // Try to match icmp (trunc nsw X), (sext Y)
+ else if (match(&Cmp, m_c_ICmp(Pred, m_NSWTrunc(m_Value(X)),
+ m_OneUse(m_ZExtOrSExt(m_Value(Y)))))) {
+ // Can fold trunc nsw + zext/sext for all predicates.
+ YIsSExt = isa<SExtInst>(Cmp.getOperand(0)) ||
+ isa<SExtInst>(Cmp.getOperand(1));
+ } else
return nullptr;
Type *TruncTy = Cmp.getOperand(0)->getType();
@@ -1518,19 +1535,7 @@ InstCombinerImpl::foldICmpTruncWithTruncOrExt(ICmpInst &Cmp,
!isDesirableIntType(X->getType()->getScalarSizeInBits()))
return nullptr;
- // Check if the trunc is unneeded.
- KnownBits KnownX = llvm::computeKnownBits(X, /*Depth*/ 0, Q);
- if (KnownX.countMaxActiveBits() > TruncBits)
- return nullptr;
-
- if (!YIsZext) {
- // If Y is also a trunc, make sure it is unneeded.
- KnownBits KnownY = llvm::computeKnownBits(Y, /*Depth*/ 0, Q);
- if (KnownY.countMaxActiveBits() > TruncBits)
- return nullptr;
- }
-
- Value *NewY = Builder.CreateZExtOrTrunc(Y, X->getType());
+ Value *NewY = Builder.CreateIntCast(Y, X->getType(), YIsSExt);
return new ICmpInst(Pred, X, NewY);
}
diff --git a/llvm/test/Transforms/InstCombine/icmp-of-trunc-ext.ll b/llvm/test/Transforms/InstCombine/icmp-of-trunc-ext.ll
index a61694919ab040..0a8bf013dc55d2 100644
--- a/llvm/test/Transforms/InstCombine/icmp-of-trunc-ext.ll
+++ b/llvm/test/Transforms/InstCombine/icmp-of-trunc-ext.ll
@@ -271,9 +271,7 @@ define i1 @icmp_trunc_x_zext_y_fail_multiuse(i32 %x, i8 %y) {
define i1 @trunc_unsigned_nuw(i16 %x, i16 %y) {
; CHECK-LABEL: @trunc_unsigned_nuw(
-; CHECK-NEXT: [[XT:%.*]] = trunc nuw i16 [[X:%.*]] to i8
-; CHECK-NEXT: [[YT:%.*]] = trunc nuw i16 [[Y:%.*]] to i8
-; CHECK-NEXT: [[C:%.*]] = icmp ult i8 [[XT]], [[YT]]
+; CHECK-NEXT: [[C:%.*]] = icmp ult i16 [[X:%.*]], [[Y:%.*]]
; CHECK-NEXT: ret i1 [[C]]
;
%xt = trunc nuw i16 %x to i8
@@ -284,9 +282,7 @@ define i1 @trunc_unsigned_nuw(i16 %x, i16 %y) {
define i1 @trunc_unsigned_nsw(i16 %x, i16 %y) {
; CHECK-LABEL: @trunc_unsigned_nsw(
-; CHECK-NEXT: [[XT:%.*]] = trunc nsw i16 [[X:%.*]] to i8
-; CHECK-NEXT: [[YT:%.*]] = trunc nsw i16 [[Y:%.*]] to i8
-; CHECK-NEXT: [[C:%.*]] = icmp ult i8 [[XT]], [[YT]]
+; CHECK-NEXT: [[C:%.*]] = icmp ult i16 [[X:%.*]], [[Y:%.*]]
; CHECK-NEXT: ret i1 [[C]]
;
%xt = trunc nsw i16 %x to i8
@@ -297,9 +293,7 @@ define i1 @trunc_unsigned_nsw(i16 %x, i16 %y) {
define i1 @trunc_unsigned_both(i16 %x, i16 %y) {
; CHECK-LABEL: @trunc_unsigned_both(
-; CHECK-NEXT: [[XT:%.*]] = trunc nuw nsw i16 [[X:%.*]] to i8
-; CHECK-NEXT: [[YT:%.*]] = trunc nuw nsw i16 [[Y:%.*]] to i8
-; CHECK-NEXT: [[C:%.*]] = icmp ult i8 [[XT]], [[YT]]
+; CHECK-NEXT: [[C:%.*]] = icmp ult i16 [[X:%.*]], [[Y:%.*]]
; CHECK-NEXT: ret i1 [[C]]
;
%xt = trunc nuw nsw i16 %x to i8
@@ -336,9 +330,7 @@ define i1 @trunc_signed_nuw(i16 %x, i16 %y) {
define i1 @trunc_signed_nsw(i16 %x, i16 %y) {
; CHECK-LABEL: @trunc_signed_nsw(
-; CHECK-NEXT: [[XT:%.*]] = trunc nsw i16 [[X:%.*]] to i8
-; CHECK-NEXT: [[YT:%.*]] = trunc nsw i16 [[Y:%.*]] to i8
-; CHECK-NEXT: [[C:%.*]] = icmp slt i8 [[XT]], [[YT]]
+; CHECK-NEXT: [[C:%.*]] = icmp slt i16 [[X:%.*]], [[Y:%.*]]
; CHECK-NEXT: ret i1 [[C]]
;
%xt = trunc nsw i16 %x to i8
@@ -349,9 +341,7 @@ define i1 @trunc_signed_nsw(i16 %x, i16 %y) {
define i1 @trunc_signed_both(i16 %x, i16 %y) {
; CHECK-LABEL: @trunc_signed_both(
-; CHECK-NEXT: [[XT:%.*]] = trunc nuw nsw i16 [[X:%.*]] to i8
-; CHECK-NEXT: [[YT:%.*]] = trunc nuw nsw i16 [[Y:%.*]] to i8
-; CHECK-NEXT: [[C:%.*]] = icmp slt i8 [[XT]], [[YT]]
+; CHECK-NEXT: [[C:%.*]] = icmp slt i16 [[X:%.*]], [[Y:%.*]]
; CHECK-NEXT: ret i1 [[C]]
;
%xt = trunc nuw nsw i16 %x to i8
@@ -375,9 +365,7 @@ define i1 @trunc_signed_either(i16 %x, i16 %y) {
define i1 @trunc_equality_nuw(i16 %x, i16 %y) {
; CHECK-LABEL: @trunc_equality_nuw(
-; CHECK-NEXT: [[XT:%.*]] = trunc nuw i16 [[X:%.*]] to i8
-; CHECK-NEXT: [[YT:%.*]] = trunc nuw i16 [[Y:%.*]] to i8
-; CHECK-NEXT: [[C:%.*]] = icmp eq i8 [[XT]], [[YT]]
+; CHECK-NEXT: [[C:%.*]] = icmp eq i16 [[X:%.*]], [[Y:%.*]]
; CHECK-NEXT: ret i1 [[C]]
;
%xt = trunc nuw i16 %x to i8
@@ -388,9 +376,7 @@ define i1 @trunc_equality_nuw(i16 %x, i16 %y) {
define i1 @trunc_equality_nsw(i16 %x, i16 %y) {
; CHECK-LABEL: @trunc_equality_nsw(
-; CHECK-NEXT: [[XT:%.*]] = trunc nsw i16 [[X:%.*]] to i8
-; CHECK-NEXT: [[YT:%.*]] = trunc nsw i16 [[Y:%.*]] to i8
-; CHECK-NEXT: [[C:%.*]] = icmp eq i8 [[XT]], [[YT]]
+; CHECK-NEXT: [[C:%.*]] = icmp eq i16 [[X:%.*]], [[Y:%.*]]
; CHECK-NEXT: ret i1 [[C]]
;
%xt = trunc nsw i16 %x to i8
@@ -401,9 +387,7 @@ define i1 @trunc_equality_nsw(i16 %x, i16 %y) {
define i1 @trunc_equality_both(i16 %x, i16 %y) {
; CHECK-LABEL: @trunc_equality_both(
-; CHECK-NEXT: [[XT:%.*]] = trunc nuw nsw i16 [[X:%.*]] to i8
-; CHECK-NEXT: [[YT:%.*]] = trunc nuw nsw i16 [[Y:%.*]] to i8
-; CHECK-NEXT: [[C:%.*]] = icmp eq i8 [[XT]], [[YT]]
+; CHECK-NEXT: [[C:%.*]] = icmp eq i16 [[X:%.*]], [[Y:%.*]]
; CHECK-NEXT: ret i1 [[C]]
;
%xt = trunc nuw nsw i16 %x to i8
@@ -427,9 +411,8 @@ define i1 @trunc_equality_either(i16 %x, i16 %y) {
define i1 @trunc_unsigned_nuw_zext(i32 %x, i8 %y) {
; CHECK-LABEL: @trunc_unsigned_nuw_zext(
-; CHECK-NEXT: [[XT:%.*]] = trunc nuw i32 [[X:%.*]] to i16
-; CHECK-NEXT: [[YE:%.*]] = zext i8 [[Y:%.*]] to i16
-; CHECK-NEXT: [[C:%.*]] = icmp ult i16 [[XT]], [[YE]]
+; CHECK-NEXT: [[TMP1:%.*]] = zext i8 [[Y:%.*]] to i32
+; CHECK-NEXT: [[C:%.*]] = icmp ugt i32 [[TMP1]], [[X:%.*]]
; CHECK-NEXT: ret i1 [[C]]
;
%xt = trunc nuw i32 %x to i16
@@ -453,9 +436,8 @@ define i1 @trunc_unsigned_nuw_sext(i32 %x, i8 %y) {
define i1 @trunc_unsigned_nsw_zext(i32 %x, i8 %y) {
; CHECK-LABEL: @trunc_unsigned_nsw_zext(
-; CHECK-NEXT: [[XT:%.*]] = trunc nsw i32 [[X:%.*]] to i16
-; CHECK-NEXT: [[YE:%.*]] = zext i8 [[Y:%.*]] to i16
-; CHECK-NEXT: [[C:%.*]] = icmp ult i16 [[XT]], [[YE]]
+; CHECK-NEXT: [[TMP1:%.*]] = zext i8 [[Y:%.*]] to i32
+; CHECK-NEXT: [[C:%.*]] = icmp ugt i32 [[TMP1]], [[X:%.*]]
; CHECK-NEXT: ret i1 [[C]]
;
%xt = trunc nsw i32 %x to i16
@@ -466,9 +448,8 @@ define i1 @trunc_unsigned_nsw_zext(i32 %x, i8 %y) {
define i1 @trunc_unsigned_nsw_sext(i32 %x, i8 %y) {
; CHECK-LABEL: @trunc_unsigned_nsw_sext(
-; CHECK-NEXT: [[XT:%.*]] = trunc nsw i32 [[X:%.*]] to i16
-; CHECK-NEXT: [[YE:%.*]] = sext i8 [[Y:%.*]] to i16
-; CHECK-NEXT: [[C:%.*]] = icmp ult i16 [[XT]], [[YE]]
+; CHECK-NEXT: [[TMP1:%.*]] = sext i8 [[Y:%.*]] to i32
+; CHECK-NEXT: [[C:%.*]] = icmp ugt i32 [[TMP1]], [[X:%.*]]
; CHECK-NEXT: ret i1 [[C]]
;
%xt = trunc nsw i32 %x to i16
@@ -479,9 +460,8 @@ define i1 @trunc_unsigned_nsw_sext(i32 %x, i8 %y) {
define i1 @trunc_signed_nsw_sext(i32 %x, i8 %y) {
; CHECK-LABEL: @trunc_signed_nsw_sext(
-; CHECK-NEXT: [[XT:%.*]] = trunc nsw i32 [[X:%.*]] to i16
-; CHECK-NEXT: [[YE:%.*]] = sext i8 [[Y:%.*]] to i16
-; CHECK-NEXT: [[C:%.*]] = icmp slt i16 [[XT]], [[YE]]
+; CHECK-NEXT: [[TMP1:%.*]] = sext i8 [[Y:%.*]] to i32
+; CHECK-NEXT: [[C:%.*]] = icmp sgt i32 [[TMP1]], [[X:%.*]]
; CHECK-NEXT: ret i1 [[C]]
;
%xt = trunc nsw i32 %x to i16
@@ -492,9 +472,8 @@ define i1 @trunc_signed_nsw_sext(i32 %x, i8 %y) {
define i1 @trunc_signed_nsw_zext(i32 %x, i8 %y) {
; CHECK-LABEL: @trunc_signed_nsw_zext(
-; CHECK-NEXT: [[XT:%.*]] = trunc nsw i32 [[X:%.*]] to i16
-; CHECK-NEXT: [[YE:%.*]] = zext i8 [[Y:%.*]] to i16
-; CHECK-NEXT: [[C:%.*]] = icmp slt i16 [[XT]], [[YE]]
+; CHECK-NEXT: [[TMP1:%.*]] = zext i8 [[Y:%.*]] to i32
+; CHECK-NEXT: [[C:%.*]] = icmp sgt i32 [[TMP1]], [[X:%.*]]
; CHECK-NEXT: ret i1 [[C]]
;
%xt = trunc nsw i32 %x to i16
@@ -531,9 +510,8 @@ define i1 @trunc_signed_nuw_zext(i32 %x, i8 %y) {
define i1 @trunc_equality_nuw_zext(i32 %x, i8 %y) {
; CHECK-LABEL: @trunc_equality_nuw_zext(
-; CHECK-NEXT: [[XT:%.*]] = trunc nuw i32 [[X:%.*]] to i16
-; CHECK-NEXT: [[YE:%.*]] = zext i8 [[Y:%.*]] to i16
-; CHECK-NEXT: [[C:%.*]] = icmp ne i16 [[XT]], [[YE]]
+; CHECK-NEXT: [[TMP1:%.*]] = zext i8 [[Y:%.*]] to i32
+; CHECK-NEXT: [[C:%.*]] = icmp ne i32 [[TMP1]], [[X:%.*]]
; CHECK-NEXT: ret i1 [[C]]
;
%xt = trunc nuw i32 %x to i16
@@ -557,9 +535,8 @@ define i1 @trunc_equality_nuw_sext(i32 %x, i8 %y) {
define i1 @trunc_equality_nsw_zext(i32 %x, i8 %y) {
; CHECK-LABEL: @trunc_equality_nsw_zext(
-; CHECK-NEXT: [[XT:%.*]] = trunc nsw i32 [[X:%.*]] to i16
-; CHECK-NEXT: [[YE:%.*]] = zext i8 [[Y:%.*]] to i16
-; CHECK-NEXT: [[C:%.*]] = icmp ne i16 [[XT]], [[YE]]
+; CHECK-NEXT: [[TMP1:%.*]] = zext i8 [[Y:%.*]] to i32
+; CHECK-NEXT: [[C:%.*]] = icmp ne i32 [[TMP1]], [[X:%.*]]
; CHECK-NEXT: ret i1 [[C]]
;
%xt = trunc nsw i32 %x to i16
@@ -570,9 +547,8 @@ define i1 @trunc_equality_nsw_zext(i32 %x, i8 %y) {
define i1 @trunc_equality_nsw_sext(i32 %x, i8 %y) {
; CHECK-LABEL: @trunc_equality_nsw_sext(
-; CHECK-NEXT: [[XT:%.*]] = trunc nsw i32 [[X:%.*]] to i16
-; CHECK-NEXT: [[YE:%.*]] = sext i8 [[Y:%.*]] to i16
-; CHECK-NEXT: [[C:%.*]] = icmp ne i16 [[XT]], [[YE]]
+; CHECK-NEXT: [[TMP1:%.*]] = sext i8 [[Y:%.*]] to i32
+; CHECK-NEXT: [[C:%.*]] = icmp ne i32 [[TMP1]], [[X:%.*]]
; CHECK-NEXT: ret i1 [[C]]
;
%xt = trunc nsw i32 %x to i16
@@ -583,9 +559,8 @@ define i1 @trunc_equality_nsw_sext(i32 %x, i8 %y) {
define i1 @trunc_equality_both_sext(i32 %x, i8 %y) {
; CHECK-LABEL: @trunc_equality_both_sext(
-; CHECK-NEXT: [[XT:%.*]] = trunc nuw nsw i32 [[X:%.*]] to i16
-; CHECK-NEXT: [[YE:%.*]] = sext i8 [[Y:%.*]] to i16
-; CHECK-NEXT: [[C:%.*]] = icmp ne i16 [[XT]], [[YE]]
+; CHECK-NEXT: [[TMP1:%.*]] = sext i8 [[Y:%.*]] to i32
+; CHECK-NEXT: [[C:%.*]] = icmp ne i32 [[TMP1]], [[X:%.*]]
; CHECK-NEXT: ret i1 [[C]]
;
%xt = trunc nuw nsw i32 %x to i16
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