[llvm] r238531 - [IR] fptrunc-of-fptrunc isn't an EliminableCastPair.

[Ahmed Bougacha]

Author: ab
Date: Thu May 28 19:04:30 2015
New Revision: 238531

URL: http://llvm.org/viewvc/llvm-project?rev=238531&view=rev
Log:
[IR] fptrunc-of-fptrunc isn't an EliminableCastPair.

Double and single rounding can produce different results.
This is the IR counterpart to r228911.

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

Modified: llvm/trunk/lib/IR/Instructions.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/IR/Instructions.cpp?rev=238531&r1=238530&r2=238531&view=diff
==============================================================================
--- llvm/trunk/lib/IR/Instructions.cpp (original)
+++ llvm/trunk/lib/IR/Instructions.cpp Thu May 28 19:04:30 2015
@@ -2120,7 +2120,7 @@ unsigned CastInst::isEliminableCastPair(
     {  0, 0, 0,99,99, 0, 0,99,99,99, 0, 3, 0}, // FPToSI         |
     { 99,99,99, 0, 0,99,99, 0, 0,99,99, 4, 0}, // UIToFP         +- firstOp
     { 99,99,99, 0, 0,99,99, 0, 0,99,99, 4, 0}, // SIToFP         |
-    { 99,99,99, 0, 0,99,99, 1, 0,99,99, 4, 0}, // FPTrunc        |
+    { 99,99,99, 0, 0,99,99, 0, 0,99,99, 4, 0}, // FPTrunc        |
     { 99,99,99, 2, 2,99,99,10, 2,99,99, 4, 0}, // FPExt          |
     {  1, 0, 0,99,99, 0, 0,99,99,99, 7, 3, 0}, // PtrToInt       |
     { 99,99,99,99,99,99,99,99,99,11,99,15, 0}, // IntToPtr       |

Modified: llvm/trunk/test/Transforms/InstCombine/fpcast.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/InstCombine/fpcast.ll?rev=238531&r1=238530&r2=238531&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/InstCombine/fpcast.ll (original)
+++ llvm/trunk/test/Transforms/InstCombine/fpcast.ll Thu May 28 19:04:30 2015
@@ -85,3 +85,11 @@ define float @test8(float %V) {
 ; CHECK-NEXT: %[[trunc:.*]] = fptrunc double %frem to float
 ; CHECK-NEXT: ret float %trunc
 }
+
+; CHECK-LABEL: @test_fptrunc_fptrunc
+; CHECK-NOT: fptrunc double {{.*}} to half
+define half @test_fptrunc_fptrunc(double %V) {
+  %t1 = fptrunc double %V to float
+  %t2 = fptrunc float %t1 to half
+  ret half %t2
+}