[PATCH] D147597: [InstCombine] Fold icmp(Positive1 * X * Y + Positive2) --> icmp(X * Y)

[Jun Zhang via Phabricator via llvm-commits]

junaire created this revision.
junaire added reviewers: RKSimon, spatel, nikic, goldstein.w.n, bcl5980.
Herald added subscribers: StephenFan, hiraditya.
Herald added a project: All.
junaire requested review of this revision.
Herald added a project: LLVM.
Herald added a subscriber: llvm-commits.

Related issue: https://github.com/llvm/llvm-project/issues/61538

Alive links:

- sge/sgt: https://alive2.llvm.org/ce/z/qKsnAF
- sle/slt: https://alive2.llvm.org/ce/z/R7hipZ

Signed-off-by: Jun Zhang <jun at junz.org>


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D147597

Files:
  llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
  llvm/test/Transforms/InstCombine/icmp.ll


Index: llvm/test/Transforms/InstCombine/icmp.ll
===================================================================
--- llvm/test/Transforms/InstCombine/icmp.ll
+++ llvm/test/Transforms/InstCombine/icmp.ll
@@ -4630,9 +4630,8 @@
 
 define i1 @mul_constant_add_constant_sge(i8 %a, i8 %b) {
 ; CHECK-LABEL: @mul_constant_add_constant_sge(
-; CHECK-NEXT:    [[MUL:%.*]] = mul nsw i8 [[A:%.*]], 42
-; CHECK-NEXT:    [[MUL1:%.*]] = mul nsw i8 [[MUL]], [[B:%.*]]
-; CHECK-NEXT:    [[CMP:%.*]] = icmp sgt i8 [[MUL1]], -1
+; CHECK-NEXT:    [[MUL2:%.*]] = mul i8 [[A:%.*]], [[B:%.*]]
+; CHECK-NEXT:    [[CMP:%.*]] = icmp sgt i8 [[MUL2]], -1
 ; CHECK-NEXT:    ret i1 [[CMP]]
 ;
   %mul = mul nsw i8 %a, 42
@@ -4644,10 +4643,8 @@
 
 define i1 @mul_constant_add_constant_sgt(i8 %a, i8 %b) {
 ; CHECK-LABEL: @mul_constant_add_constant_sgt(
-; CHECK-NEXT:    [[MUL:%.*]] = mul nsw i8 [[A:%.*]], 42
-; CHECK-NEXT:    [[MUL1:%.*]] = mul nsw i8 [[MUL]], [[B:%.*]]
-; CHECK-NEXT:    [[ADD:%.*]] = or i8 [[MUL1]], 24
-; CHECK-NEXT:    [[CMP:%.*]] = icmp sgt i8 [[ADD]], 0
+; CHECK-NEXT:    [[MUL2:%.*]] = mul i8 [[A:%.*]], [[B:%.*]]
+; CHECK-NEXT:    [[CMP:%.*]] = icmp sgt i8 [[MUL2]], -1
 ; CHECK-NEXT:    ret i1 [[CMP]]
 ;
   %mul = mul nsw i8 %a, 42
@@ -4659,10 +4656,8 @@
 
 define i1 @mul_constant_add_constant_sle(i8 %a, i8 %b) {
 ; CHECK-LABEL: @mul_constant_add_constant_sle(
-; CHECK-NEXT:    [[MUL:%.*]] = mul nsw i8 [[A:%.*]], 42
-; CHECK-NEXT:    [[MUL1:%.*]] = mul nsw i8 [[MUL]], [[B:%.*]]
-; CHECK-NEXT:    [[ADD:%.*]] = or i8 [[MUL1]], 24
-; CHECK-NEXT:    [[CMP:%.*]] = icmp slt i8 [[ADD]], 1
+; CHECK-NEXT:    [[MUL2:%.*]] = mul i8 [[A:%.*]], [[B:%.*]]
+; CHECK-NEXT:    [[CMP:%.*]] = icmp slt i8 [[MUL2]], 0
 ; CHECK-NEXT:    ret i1 [[CMP]]
 ;
   %mul = mul nsw i8 %a, 42
@@ -4674,9 +4669,8 @@
 
 define i1 @mul_constant_add_constant_slt(i8 %a, i8 %b) {
 ; CHECK-LABEL: @mul_constant_add_constant_slt(
-; CHECK-NEXT:    [[MUL:%.*]] = mul nsw i8 [[A:%.*]], 42
-; CHECK-NEXT:    [[MUL1:%.*]] = mul nsw i8 [[MUL]], [[B:%.*]]
-; CHECK-NEXT:    [[CMP:%.*]] = icmp slt i8 [[MUL1]], 0
+; CHECK-NEXT:    [[MUL2:%.*]] = mul i8 [[A:%.*]], [[B:%.*]]
+; CHECK-NEXT:    [[CMP:%.*]] = icmp slt i8 [[MUL2]], 0
 ; CHECK-NEXT:    ret i1 [[CMP]]
 ;
   %mul = mul nsw i8 %a, 42
Index: llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
===================================================================
--- llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
+++ llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
@@ -1338,11 +1338,39 @@
     if (Instruction *Res = processUGT_ADDCST_ADD(Cmp, A, B, CI2, CI, *this))
       return Res;
 
-  // icmp(phi(C1, C2, ...), C) -> phi(icmp(C1, C), icmp(C2, C), ...).
   Constant *C = dyn_cast<Constant>(Op1);
   if (!C)
     return nullptr;
 
+  // Fold icmp (Positive1 * a * b + Positive2) --> icmp (a * b)
+  if (match(Op0,
+            m_c_Or(m_c_Mul(m_c_Mul(m_Value(A), m_ConstantInt(CI)), m_Value(B)),
+                   m_ConstantInt(CI2)))) {
+    if (CI->getValue().isStrictlyPositive() &&
+        CI2->getValue().isStrictlyPositive()) {
+      auto Relax = [&](CmpInst::Predicate Pred, Value *A, Value *B) {
+        Value *Mul = Builder.CreateMul(A, B, "mul");
+        Value *NewCmp = Builder.CreateICmp(
+            Pred, Mul, ConstantInt::getNullValue(A->getType()));
+        return replaceInstUsesWith(Cmp, NewCmp);
+      };
+      CmpInst::Predicate NewPred;
+      switch (Pred) {
+      case ICmpInst::ICMP_SGE:
+      case ICmpInst::ICMP_SGT:
+        NewPred = ICmpInst::ICMP_SGE;
+        return Relax(NewPred, A, B);
+      case ICmpInst::ICMP_SLT:
+      case ICmpInst::ICMP_SLE:
+        NewPred = ICmpInst::ICMP_SLT;
+        return Relax(NewPred, A, B);
+      default:
+        break;
+      }
+    }
+  }
+
+  // icmp(phi(C1, C2, ...), C) -> phi(icmp(C1, C), icmp(C2, C), ...).
   if (auto *Phi = dyn_cast<PHINode>(Op0))
     if (all_of(Phi->operands(), [](Value *V) { return isa<Constant>(V); })) {
       Type *Ty = Cmp.getType();


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