Fix missed optimization opportunity when analyzing cast of mul and select.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@53151 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/Transforms/Scalar/InstructionCombining.cpp b/lib/Transforms/Scalar/InstructionCombining.cpp
index 5d75489d14f1375cba0188db81dc264efcc9a59c..8c3f2d5a74a9cd290e6ce43adc1c1b7b0c037b0a 100644 (file)
--- a/lib/Transforms/Scalar/InstructionCombining.cpp
+++ b/lib/Transforms/Scalar/InstructionCombining.cpp
@@ -6917,6 +6917,7 @@ bool InstCombiner::CanEvaluateInDifferentType(Value *V, const IntegerType *Ty,
   switch (I->getOpcode()) {
   case Instruction::Add:
   case Instruction::Sub:
+  case Instruction::Mul:
   case Instruction::And:
   case Instruction::Or:
   case Instruction::Xor:
@@ -6926,14 +6927,6 @@ bool InstCombiner::CanEvaluateInDifferentType(Value *V, const IntegerType *Ty,
            CanEvaluateInDifferentType(I->getOperand(1), Ty, CastOpc,
                                       NumCastsRemoved);
 
-  case Instruction::Mul:
-    // A multiply can be truncated by truncating its operands.
-    return Ty->getBitWidth() < OrigTy->getBitWidth() && 
-           CanEvaluateInDifferentType(I->getOperand(0), Ty, CastOpc,
-                                      NumCastsRemoved) &&
-           CanEvaluateInDifferentType(I->getOperand(1), Ty, CastOpc,
-                                      NumCastsRemoved);
-
   case Instruction::Shl:
     // If we are truncating the result of this SHL, and if it's a shift of a
     // constant amount, we can always perform a SHL in a smaller type.
@@ -6970,7 +6963,13 @@ bool InstCombiner::CanEvaluateInDifferentType(Value *V, const IntegerType *Ty,
     if (I->getOpcode() == CastOpc)
       return true;
     break;
-      
+  case Instruction::Select: {
+    SelectInst *SI = cast<SelectInst>(I);
+    return CanEvaluateInDifferentType(SI->getTrueValue(), Ty, CastOpc,
+                                      NumCastsRemoved) &&
+           CanEvaluateInDifferentType(SI->getFalseValue(), Ty, CastOpc,
+                                      NumCastsRemoved);
+  }
   case Instruction::PHI: {
     // We can change a phi if we can change all operands.
     PHINode *PN = cast<PHINode>(I);
@@ -7028,6 +7027,12 @@ Value *InstCombiner::EvaluateInDifferentType(Value *V, const Type *Ty,
     Res = CastInst::Create(cast<CastInst>(I)->getOpcode(), I->getOperand(0),
                            Ty);
     break;
+  case Instruction::Select: {
+    Value *True = EvaluateInDifferentType(I->getOperand(1), Ty, isSigned);
+    Value *False = EvaluateInDifferentType(I->getOperand(2), Ty, isSigned);
+    Res = SelectInst::Create(I->getOperand(0), True, False);
+    break;
+  }
   case Instruction::PHI: {
     PHINode *OPN = cast<PHINode>(I);
     PHINode *NPN = PHINode::Create(Ty);

diff --git a/test/Transforms/InstCombine/cast-mul-select.ll b/test/Transforms/InstCombine/cast-mul-select.ll
new file mode 100644 (file)
index 0000000..76e9b24
--- /dev/null
+++ b/test/Transforms/InstCombine/cast-mul-select.ll
@@ -0,0 +1,29 @@
+; RUN: llvm-as < %s | opt -instcombine | llvm-dis | notcast
+
+define i32 @mul(i32 %x, i32 %y) {
+  %A = trunc i32 %x to i8
+  %B = trunc i32 %y to i8
+  %C = mul i8 %A, %B
+  %D = zext i8 %C to i32
+  ret i32 %D
+}
+
+define i32 @select1(i1 %cond, i32 %x, i32 %y, i32 %z) {
+  %A = trunc i32 %x to i8
+  %B = trunc i32 %y to i8
+  %C = trunc i32 %z to i8
+  %D = add i8 %A, %B
+  %E = select i1 %cond, i8 %C, i8 %D
+  %F = zext i8 %E to i32
+  ret i32 %F
+}
+
+define i8 @select2(i1 %cond, i8 %x, i8 %y, i8 %z) {
+  %A = zext i8 %x to i32
+  %B = zext i8 %y to i32
+  %C = zext i8 %z to i32
+  %D = add i32 %A, %B
+  %E = select i1 %cond, i32 %C, i32 %D
+  %F = trunc i32 %E to i8
+  ret i8 %F
+}