[llvm] r235364 - InstCombine: fold (sitofp (zext x)) to (uitofp x)

[Fiona Glaser]

Author: escha
Date: Mon Apr 20 19:05:41 2015
New Revision: 235364

URL: http://llvm.org/viewvc/llvm-project?rev=235364&view=rev
Log:
InstCombine: fold (sitofp (zext x)) to (uitofp x)

This is okay because the zext guarantees the high bit is zero,
and so the value is unsigned.

Modified:
    llvm/trunk/lib/IR/Instructions.cpp
    llvm/trunk/test/Transforms/InstCombine/cast.ll

Modified: llvm/trunk/lib/IR/Instructions.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/IR/Instructions.cpp?rev=235364&r1=235363&r2=235364&view=diff
==============================================================================
--- llvm/trunk/lib/IR/Instructions.cpp (original)
+++ llvm/trunk/lib/IR/Instructions.cpp Mon Apr 20 19:05:41 2015
@@ -2118,7 +2118,7 @@ unsigned CastInst::isEliminableCastPair(
     // N  X  X  U  S  F  F  N  X  N  2  V  V   |
     // C  T  T  I  I  P  P  C  T  T  P  T  T  -+
     {  1, 0, 0,99,99, 0, 0,99,99,99, 0, 3, 0}, // Trunc         -+
-    {  8, 1, 9,99,99, 2, 0,99,99,99, 2, 3, 0}, // ZExt           |
+    {  8, 1, 9,99,99, 2,17,99,99,99, 2, 3, 0}, // ZExt           |
     {  8, 0, 1,99,99, 0, 2,99,99,99, 0, 3, 0}, // SExt           |
     {  0, 0, 0,99,99, 0, 0,99,99,99, 0, 3, 0}, // FPToUI         |
     {  0, 0, 0,99,99, 0, 0,99,99,99, 0, 3, 0}, // FPToSI         |
@@ -2285,6 +2285,9 @@ unsigned CastInst::isEliminableCastPair(
         "Illegal bitcast, ptrtoint sequence!");
       // Allowed, use second cast's opcode
       return secondOp;
+    case 17:
+      // (sitofp (zext x)) -> (uitofp x)
+      return Instruction::UIToFP;
     case 99: 
       // Cast combination can't happen (error in input). This is for all cases
       // where the MidTy is not the same for the two cast instructions.

Modified: llvm/trunk/test/Transforms/InstCombine/cast.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/InstCombine/cast.ll?rev=235364&r1=235363&r2=235364&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/InstCombine/cast.ll (original)
+++ llvm/trunk/test/Transforms/InstCombine/cast.ll Mon Apr 20 19:05:41 2015
@@ -1104,3 +1104,12 @@ define i32 @PR21388(i32* %v) {
 ; CHECK-NEXT: %[[sext:.*]] = sext i1 %[[icmp]] to i32
 ; CHECK-NEXT: ret i32 %[[sext]]
 }
+
+define float @sitofp_zext(i16 %a) {
+; CHECK-LABEL: @sitofp_zext(
+; CHECK-NEXT: %[[sitofp:.*]] = uitofp i16 %a to float
+; CHECK-NEXT: ret float %[[sitofp]]
+  %zext = zext i16 %a to i32
+  %sitofp = sitofp i32 %zext to float
+  ret float %sitofp
+}