[llvm-commits] [llvm] r46244 - in /llvm/trunk: lib/Transforms/Scalar/InstructionCombining.cpp test/Transforms/InstCombine/2008-01-21-MulTrunc.ll

[Nick Lewycky]

Author: nicholas
Date: Mon Jan 21 23:08:48 2008
New Revision: 46244

URL: http://llvm.org/viewvc/llvm-project?rev=46244&view=rev
Log:
Multiply can be evaluated in a different type, so long as the target type has
a smaller bitwidth.

Added:
    llvm/trunk/test/Transforms/InstCombine/2008-01-21-MulTrunc.ll
Modified:
    llvm/trunk/lib/Transforms/Scalar/InstructionCombining.cpp

Modified: llvm/trunk/lib/Transforms/Scalar/InstructionCombining.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Scalar/InstructionCombining.cpp?rev=46244&r1=46243&r2=46244&view=diff

==============================================================================
--- llvm/trunk/lib/Transforms/Scalar/InstructionCombining.cpp (original)
+++ llvm/trunk/lib/Transforms/Scalar/InstructionCombining.cpp Mon Jan 21 23:08:48 2008
@@ -6512,6 +6512,15 @@
            CanEvaluateInDifferentType(I->getOperand(1), Ty, CastOpc,
                                       NumCastsRemoved);
 
+  case Instruction::Mul:
+    break;
+    // 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.
@@ -6571,6 +6580,7 @@
   switch (I->getOpcode()) {
   case Instruction::Add:
   case Instruction::Sub:
+  case Instruction::Mul:
   case Instruction::And:
   case Instruction::Or:
   case Instruction::Xor:

Added: llvm/trunk/test/Transforms/InstCombine/2008-01-21-MulTrunc.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/InstCombine/2008-01-21-MulTrunc.ll?rev=46244&view=auto

==============================================================================
--- llvm/trunk/test/Transforms/InstCombine/2008-01-21-MulTrunc.ll (added)
+++ llvm/trunk/test/Transforms/InstCombine/2008-01-21-MulTrunc.ll Mon Jan 21 23:08:48 2008
@@ -0,0 +1,11 @@
+; RUN: llvm-as < %s | opt -instcombine | llvm-dis | notcast
+
+define i16 @test1(i16 %a) {
+        %tmp = zext i16 %a to i32               ; <i32> [#uses=2]
+        %tmp21 = lshr i32 %tmp, 8               ; <i32> [#uses=1]
+        %tmp5 = mul i32 %tmp, 5         ; <i32> [#uses=1]
+        %tmp.upgrd.32 = or i32 %tmp21, %tmp5            ; <i32> [#uses=1]
+        %tmp.upgrd.3 = trunc i32 %tmp.upgrd.32 to i16           ; <i16> [#uses=1]
+        ret i16 %tmp.upgrd.3
+}
+