From 7dd540ee2469c7c931360ca0aa196d71b54b3e72 Mon Sep 17 00:00:00 2001
From: Chris Lattner <sabre@nondot.org>
Date: Sun, 10 Jan 2010 20:30:41 +0000
Subject: [PATCH] teach sext optimization to handle truncs from types that are
 not the dest of the sext.

llvm-svn: 93128
---
 .../InstCombine/InstCombineCasts.cpp          |  7 ++---
 llvm/test/Transforms/InstCombine/cast.ll      | 26 +++++++++++++++++++
 2 files changed, 30 insertions(+), 3 deletions(-)

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp b/llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp
index e2e74c1e5d54..49b2e22a6815 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp
@@ -799,6 +799,10 @@ static bool CanEvaluateSExtd(Value *V, const Type *Ty, TargetData *TD) {
   if (!I->hasOneUse()) return false;
 
   switch (I->getOpcode()) {
+  case Instruction::SExt:  // sext(sext(x)) -> sext(x)
+  case Instruction::ZExt:  // sext(zext(x)) -> zext(x)
+  case Instruction::Trunc: // sext(trunc(x)) -> trunc(x) or sext(x)
+    return true;
   case Instruction::And:
   case Instruction::Or:
   case Instruction::Xor:
@@ -813,9 +817,6 @@ static bool CanEvaluateSExtd(Value *V, const Type *Ty, TargetData *TD) {
   //case Instruction::LShr:  TODO
   //case Instruction::Trunc: TODO
       
-  case Instruction::SExt: // sext(sext(x)) -> sext(x)
-  case Instruction::ZExt: // sext(zext(x)) -> zext(x)
-    return true;
   case Instruction::Select:
     return CanEvaluateSExtd(I->getOperand(1), Ty, TD) &&
            CanEvaluateSExtd(I->getOperand(2), Ty, TD);
diff --git a/llvm/test/Transforms/InstCombine/cast.ll b/llvm/test/Transforms/InstCombine/cast.ll
index 8424967e11ab..d624f342b9be 100644
--- a/llvm/test/Transforms/InstCombine/cast.ll
+++ b/llvm/test/Transforms/InstCombine/cast.ll
@@ -523,3 +523,29 @@ define i64 @test53(i32 %A) {
 ; CHECK-NEXT: %D = and i64 %C, 40186
 ; CHECK-NEXT: ret i64 %D
 }
+
+define i32 @test54(i64 %A) {
+  %B = trunc i64 %A to i16
+  %C = or i16 %B, -32574
+  %D = and i16 %C, -25350
+  %E = sext i16 %D to i32
+  ret i32 %E
+; CHECK: @test54
+; CHECK-NEXT: %B = trunc i64 %A to i32
+; CHECK-NEXT: %C = or i32 %B, -32574
+; CHECK-NEXT: %D = and i32 %C, -25350
+; CHECK-NEXT: ret i32 %D
+}
+
+define i64 @test55(i32 %A) {
+  %B = trunc i32 %A to i16
+  %C = or i16 %B, -32574
+  %D = and i16 %C, -25350
+  %E = sext i16 %D to i64
+  ret i64 %E
+; CHECK: @test55
+; CHECK-NEXT: %B = zext i32 %A to i64
+; CHECK-NEXT: %C = or i64 %B, -32574
+; CHECK-NEXT: %D = and i64 %C, -25350
+; CHECK-NEXT: ret i64 %D
+}
\ No newline at end of file