[llvm] 6cf10b7 - [InstCombine] Fold srem(X, PowerOf2) == C into (X & Mask) == C for positive C

[Alexander Shaposhnikov via llvm-commits]

Author: Alexander Shaposhnikov
Date: 2022-04-03T03:57:05Z
New Revision: 6cf10b7e6e839fea1843ba365a6a26e77b52e251

URL: https://github.com/llvm/llvm-project/commit/6cf10b7e6e839fea1843ba365a6a26e77b52e251
DIFF: https://github.com/llvm/llvm-project/commit/6cf10b7e6e839fea1843ba365a6a26e77b52e251.diff

LOG: [InstCombine] Fold srem(X, PowerOf2) == C into (X & Mask) == C for positive C

This diff extends InstCombinerImpl::foldICmpSRemConstant to handle the cases
srem(X, PowerOf2) == C and
srem(X, PowerOf2) != C
for positive C.
This addresses the issue https://github.com/llvm/llvm-project/issues/54650

Differential revision: https://reviews.llvm.org/D122942

Test plan: make check-all

Added: 
    

Modified: 
    llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
    llvm/test/Transforms/InstCombine/rem.ll

Removed: 
    


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diff  --git a/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp b/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
index 39c20ec06ca29..3e6a2f0d108a1 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
@@ -2335,7 +2335,8 @@ Instruction *InstCombinerImpl::foldICmpSRemConstant(ICmpInst &Cmp,
   // constant power-of-2 value:
   // (X % pow2C) sgt/slt 0
   const ICmpInst::Predicate Pred = Cmp.getPredicate();
-  if (Pred != ICmpInst::ICMP_SGT && Pred != ICmpInst::ICMP_SLT)
+  if (Pred != ICmpInst::ICMP_SGT && Pred != ICmpInst::ICMP_SLT &&
+      Pred != ICmpInst::ICMP_EQ && Pred != ICmpInst::ICMP_NE)
     return nullptr;
 
   // TODO: The one-use check is standard because we do not typically want to
@@ -2345,7 +2346,15 @@ Instruction *InstCombinerImpl::foldICmpSRemConstant(ICmpInst &Cmp,
     return nullptr;
 
   const APInt *DivisorC;
-  if (!C.isZero() || !match(SRem->getOperand(1), m_Power2(DivisorC)))
+  if (!match(SRem->getOperand(1), m_Power2(DivisorC)))
+    return nullptr;
+
+  // For cmp_sgt/cmp_slt only zero valued C is handled.
+  // For cmp_eq/cmp_ne only positive valued C is handled.
+  if (((Pred == ICmpInst::ICMP_SGT || Pred == ICmpInst::ICMP_SLT) &&
+       !C.isZero()) ||
+      ((Pred == ICmpInst::ICMP_EQ || Pred == ICmpInst::ICMP_NE) &&
+       !C.isStrictlyPositive()))
     return nullptr;
 
   // Mask off the sign bit and the modulo bits (low-bits).
@@ -2354,6 +2363,9 @@ Instruction *InstCombinerImpl::foldICmpSRemConstant(ICmpInst &Cmp,
   Constant *MaskC = ConstantInt::get(Ty, SignMask | (*DivisorC - 1));
   Value *And = Builder.CreateAnd(SRem->getOperand(0), MaskC);
 
+  if (Pred == ICmpInst::ICMP_EQ || Pred == ICmpInst::ICMP_NE)
+    return new ICmpInst(Pred, And, ConstantInt::get(Ty, C));
+
   // For 'is positive?' check that the sign-bit is clear and at least 1 masked
   // bit is set. Example:
   // (i8 X % 32) s> 0 --> (X & 159) s> 0

diff  --git a/llvm/test/Transforms/InstCombine/rem.ll b/llvm/test/Transforms/InstCombine/rem.ll
index b52803ae5da42..63122363b7a81 100644
--- a/llvm/test/Transforms/InstCombine/rem.ll
+++ b/llvm/test/Transforms/InstCombine/rem.ll
@@ -742,7 +742,7 @@ define i1 @test28(i32 %A) {
 
 define i1 @positive_and_odd_eq(i32 %A) {
 ; CHECK-LABEL: @positive_and_odd_eq(
-; CHECK-NEXT:    [[B:%.*]] = srem i32 [[A:%.*]], 2
+; CHECK-NEXT:    [[B:%.*]] = and i32 [[A:%.*]], -2147483647
 ; CHECK-NEXT:    [[C:%.*]] = icmp eq i32 [[B]], 1
 ; CHECK-NEXT:    ret i1 [[C]]
 ;
@@ -764,7 +764,7 @@ define i1 @negative_and_odd_eq(i32 %A) {
 
 define i1 @positive_and_odd_ne(i32 %A) {
 ; CHECK-LABEL: @positive_and_odd_ne(
-; CHECK-NEXT:    [[B:%.*]] = srem i32 [[A:%.*]], 2
+; CHECK-NEXT:    [[B:%.*]] = and i32 [[A:%.*]], -2147483647
 ; CHECK-NEXT:    [[C:%.*]] = icmp ne i32 [[B]], 1
 ; CHECK-NEXT:    ret i1 [[C]]
 ;