GlobalISel: avoid inserting redundant COPYs for bitcasts.

If the value produced by the bitcast hasn't been referenced yet, we can simply
reuse the input register avoiding an unnecessary COPY instruction.

llvm-svn: 278245

diff --git a/llvm/lib/CodeGen/GlobalISel/IRTranslator.cpp b/llvm/lib/CodeGen/GlobalISel/IRTranslator.cpp
index a5f62cf..4ea0951 100644 (file)
--- a/llvm/lib/CodeGen/GlobalISel/IRTranslator.cpp
+++ b/llvm/lib/CodeGen/GlobalISel/IRTranslator.cpp
@@ -166,8 +166,11 @@ bool IRTranslator::translateStore(const StoreInst &SI) {
 
 bool IRTranslator::translateBitCast(const CastInst &CI) {
   if (LLT{*CI.getDestTy()} == LLT{*CI.getSrcTy()}) {
-    MIRBuilder.buildCopy(getOrCreateVReg(CI),
-                         getOrCreateVReg(*CI.getOperand(0)));
+    unsigned &Reg = ValToVReg[&CI];
+    if (Reg)
+      MIRBuilder.buildCopy(Reg, getOrCreateVReg(*CI.getOperand(0)));
+    else
+      Reg = getOrCreateVReg(*CI.getOperand(0));
     return true;
   }
   return translateCast(TargetOpcode::G_BITCAST, CI);

diff --git a/llvm/test/CodeGen/AArch64/GlobalISel/arm64-irtranslator.ll b/llvm/test/CodeGen/AArch64/GlobalISel/arm64-irtranslator.ll
index e63b851..f036d12 100644 (file)
--- a/llvm/test/CodeGen/AArch64/GlobalISel/arm64-irtranslator.ll
+++ b/llvm/test/CodeGen/AArch64/GlobalISel/arm64-irtranslator.ll
@@ -214,14 +214,33 @@ define i64* @inttoptr(i64 %a) {
 
 ; CHECK-LABEL: name: trivial_bitcast
 ; CHECK: [[ARG1:%[0-9]+]](64) = COPY %x0
-; CHECK: [[RES:%[0-9]+]](64) = COPY [[ARG1]]
-; CHECK: %x0 = COPY [[RES]]
+; CHECK: %x0 = COPY [[ARG1]]
 ; CHECK: RET_ReallyLR implicit %x0
 define i64* @trivial_bitcast(i8* %a) {
   %val = bitcast i8* %a to i64*
   ret i64* %val
 }
 
+; CHECK-LABEL: name: trivial_bitcast_with_copy
+; CHECK:     [[A:%[0-9]+]](64) = COPY %x0
+; CHECK:     G_BR unsized %[[CAST:bb\.[0-9]+]]
+
+; CHECK: [[CAST]]:
+; CHECK:     {{%[0-9]+}}(64) = COPY [[A]]
+; CHECK:     G_BR unsized %[[END:bb\.[0-9]+]]
+
+; CHECK: [[END]]:
+define i64* @trivial_bitcast_with_copy(i8* %a) {
+  br label %cast
+
+end:
+  ret i64* %val
+
+cast:
+  %val = bitcast i8* %a to i64*
+  br label %end
+}
+
 ; CHECK-LABEL: name: bitcast
 ; CHECK: [[ARG1:%[0-9]+]](64) = COPY %x0
 ; CHECK: [[RES1:%[0-9]+]](64) = G_BITCAST { <2 x s32>, s64 } [[ARG1]]