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-rw-r--r--lib/Transforms/Scalar/InstructionCombining.cpp14
-rw-r--r--test/Transforms/InstCombine/trunc-mask-ext.ll23
2 files changed, 37 insertions, 0 deletions
diff --git a/lib/Transforms/Scalar/InstructionCombining.cpp b/lib/Transforms/Scalar/InstructionCombining.cpp
index 170b476..bf287f2 100644
--- a/lib/Transforms/Scalar/InstructionCombining.cpp
+++ b/lib/Transforms/Scalar/InstructionCombining.cpp
@@ -8564,6 +8564,20 @@ Instruction *InstCombiner::visitZExt(ZExtInst &CI) {
}
}
+ // zext(trunc(t) & C) -> (t & C) if C is a mask.
+ if (SrcI && SrcI->getOpcode() == Instruction::And && SrcI->hasOneUse())
+ if (ConstantInt *C = dyn_cast<ConstantInt>(SrcI->getOperand(1)))
+ if (TruncInst *TI = dyn_cast<TruncInst>(SrcI->getOperand(0))) {
+ Value *TI0 = TI->getOperand(0);
+ if (TI0->getType() == CI.getType()) {
+ unsigned TO = C->getValue().countTrailingOnes();
+ if (APIntOps::isMask(TO, C->getValue()))
+ return
+ BinaryOperator::Create(Instruction::And, TI0,
+ ConstantExpr::getZExt(C, CI.getType()));
+ }
+ }
+
return 0;
}
diff --git a/test/Transforms/InstCombine/trunc-mask-ext.ll b/test/Transforms/InstCombine/trunc-mask-ext.ll
new file mode 100644
index 0000000..1499947
--- /dev/null
+++ b/test/Transforms/InstCombine/trunc-mask-ext.ll
@@ -0,0 +1,23 @@
+; RUN: llvm-as < %s | opt -instcombine | llvm-dis > %t
+; RUN: not grep zext %t
+; RUN: not grep sext %t
+
+; Instcombine should be able to eliminate both ext casts.
+
+declare void @use(i32)
+
+define i64 @foo(i64 %a) {
+ %b = trunc i64 %a to i32
+ %c = and i32 %b, 15
+ %d = zext i32 %c to i64
+ call void @use(i32 %b)
+ ret i64 %d
+}
+define i64 @bar(i64 %a) {
+ %b = trunc i64 %a to i32
+ %c = shl i32 %b, 4
+ %q = ashr i32 %c, 4
+ %d = sext i32 %q to i64
+ call void @use(i32 %b)
+ ret i64 %d
+}