[llvm] 0213c6d - [InstCombine] Use DL-aware constant folding for phi compare

[Nikita Popov via llvm-commits]

Author: Nikita Popov
Date: 2023-06-01T16:02:36+02:00
New Revision: 0213c6d0df1e073b046a3cb6d46c1808ddfa423e

URL: https://github.com/llvm/llvm-project/commit/0213c6d0df1e073b046a3cb6d46c1808ddfa423e
DIFF: https://github.com/llvm/llvm-project/commit/0213c6d0df1e073b046a3cb6d46c1808ddfa423e.diff

LOG: [InstCombine] Use DL-aware constant folding for phi compare

Serves the dual purpose of avoiding an extra InstCombine iteration
for the DL-aware folding and removing one icmp constexpr use.

Added: 
    

Modified: 
    llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
    llvm/test/Transforms/InstCombine/icmp-constant-phi.ll
    llvm/test/Transforms/InstCombine/indexed-gep-compares.ll

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp b/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
index 7fb3f16b346b..b11f13ab40e1 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
@@ -1382,17 +1382,18 @@ Instruction *InstCombinerImpl::foldICmpWithConstant(ICmpInst &Cmp) {
 
   if (auto *Phi = dyn_cast<PHINode>(Op0))
     if (all_of(Phi->operands(), [](Value *V) { return isa<Constant>(V); })) {
-      Type *Ty = Cmp.getType();
-      Builder.SetInsertPoint(Phi);
-      PHINode *NewPhi =
-          Builder.CreatePHI(Ty, Phi->getNumOperands());
-      for (BasicBlock *Predecessor : predecessors(Phi->getParent())) {
-        auto *Input =
-            cast<Constant>(Phi->getIncomingValueForBlock(Predecessor));
-        auto *BoolInput = ConstantExpr::getCompare(Pred, Input, C);
-        NewPhi->addIncoming(BoolInput, Predecessor);
+      SmallVector<Constant *> Ops;
+      for (Value *V : Phi->incoming_values()) {
+        Constant *Res =
+            ConstantFoldCompareInstOperands(Pred, cast<Constant>(V), C, DL);
+        if (!Res)
+          return nullptr;
+        Ops.push_back(Res);
       }
-      NewPhi->takeName(&Cmp);
+      Builder.SetInsertPoint(Phi);
+      PHINode *NewPhi = Builder.CreatePHI(Cmp.getType(), Phi->getNumOperands());
+      for (auto [V, Pred] : zip(Ops, Phi->blocks()))
+        NewPhi->addIncoming(V, Pred);
       return replaceInstUsesWith(Cmp, NewPhi);
     }
 

diff  --git a/llvm/test/Transforms/InstCombine/icmp-constant-phi.ll b/llvm/test/Transforms/InstCombine/icmp-constant-phi.ll
index 050033b93eda..95e1af4e7ee5 100644
--- a/llvm/test/Transforms/InstCombine/icmp-constant-phi.ll
+++ b/llvm/test/Transforms/InstCombine/icmp-constant-phi.ll
@@ -166,7 +166,7 @@ define <2 x i1> @test_ne_int_vector(i1 %cond) {
 ; CHECK:       if.false:
 ; CHECK-NEXT:    br label [[MERGE]]
 ; CHECK:       merge:
-; CHECK-NEXT:    [[COMPARE:%.*]] = phi <2 x i1> [ <i1 true, i1 false>, [[IF_FALSE]] ], [ <i1 false, i1 true>, [[IF_TRUE]] ]
+; CHECK-NEXT:    [[COMPARE:%.*]] = phi <2 x i1> [ <i1 false, i1 true>, [[IF_TRUE]] ], [ <i1 true, i1 false>, [[IF_FALSE]] ]
 ; CHECK-NEXT:    br label [[EXIT:%.*]]
 ; CHECK:       exit:
 ; CHECK-NEXT:    ret <2 x i1> [[COMPARE]]

diff  --git a/llvm/test/Transforms/InstCombine/indexed-gep-compares.ll b/llvm/test/Transforms/InstCombine/indexed-gep-compares.ll
index c894587d24fc..6490a94a5270 100644
--- a/llvm/test/Transforms/InstCombine/indexed-gep-compares.ll
+++ b/llvm/test/Transforms/InstCombine/indexed-gep-compares.ll
@@ -226,7 +226,7 @@ define i1 @test7() {
 ; CHECK-NEXT:  entry:
 ; CHECK-NEXT:    br label [[BB7:%.*]]
 ; CHECK:       bb7:
-; CHECK-NEXT:    [[CMP:%.*]] = phi i1 [ true, [[BB7]] ], [ false, [[ENTRY:%.*]] ]
+; CHECK-NEXT:    [[CMP:%.*]] = phi i1 [ false, [[ENTRY:%.*]] ], [ true, [[BB7]] ]
 ; CHECK-NEXT:    br i1 [[CMP]], label [[BB10:%.*]], label [[BB7]]
 ; CHECK:       bb10:
 ; CHECK-NEXT:    ret i1 [[CMP]]