From a392c788be3ddf925d460c3098c07e882bcf31bf Mon Sep 17 00:00:00 2001
From: Dan Gohman <gohman@apple.com>
Date: Wed, 17 Jun 2009 23:17:05 +0000
Subject: [PATCH] Instcombine zext(trunc(x) & mask) to x&mask, even if the
 trunc has multiple users.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@73656 91177308-0d34-0410-b5e6-96231b3b80d8
---
 .../Scalar/InstructionCombining.cpp           | 14 +++++++++++
 test/Transforms/InstCombine/trunc-mask-ext.ll | 23 +++++++++++++++++++
 2 files changed, 37 insertions(+)
 create mode 100644 test/Transforms/InstCombine/trunc-mask-ext.ll

diff --git a/lib/Transforms/Scalar/InstructionCombining.cpp b/lib/Transforms/Scalar/InstructionCombining.cpp
index 170b47694af..bf287f2c680 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 00000000000..1499947cc07
--- /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
+}