[llvm-commits] [llvm] r123121 - in /llvm/trunk: lib/Transforms/InstCombine/InstCombineSelect.cpp test/Transforms/InstCombine/select.ll

[Tobias Grosser]

Author: grosser
Date: Sun Jan  9 10:00:11 2011
New Revision: 123121

URL: http://llvm.org/viewvc/llvm-project?rev=123121&view=rev
Log:
Instcombine: Fix pattern where the sext did not dominate the icmp using it

Modified:
    llvm/trunk/lib/Transforms/InstCombine/InstCombineSelect.cpp
    llvm/trunk/test/Transforms/InstCombine/select.ll

Modified: llvm/trunk/lib/Transforms/InstCombine/InstCombineSelect.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/InstCombine/InstCombineSelect.cpp?rev=123121&r1=123120&r2=123121&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/InstCombine/InstCombineSelect.cpp (original)
+++ llvm/trunk/lib/Transforms/InstCombine/InstCombineSelect.cpp Sun Jan  9 10:00:11 2011
@@ -281,8 +281,8 @@
   Value *FalseVal = SI.getFalseValue();
 
   // Check cases where the comparison is with a constant that
-  // can be adjusted to fit the min/max idiom. We may edit ICI in
-  // place here, so make sure the select is the only user.
+  // can be adjusted to fit the min/max idiom. We may move or edit ICI
+  // here, so make sure the select is the only user.
   if (ICI->hasOneUse())
     if (ConstantInt *CI = dyn_cast<ConstantInt>(CmpRHS)) {
       // X < MIN ? T : F  -->  F
@@ -364,6 +364,11 @@
         ICI->setOperand(1, CmpRHS);
         SI.setOperand(1, TrueVal);
         SI.setOperand(2, FalseVal);
+
+        // Move ICI instruction right before the select instruction. Otherwise
+        // the sext/zext value may be defined after the ICI instruction uses it.
+        ICI->moveBefore(&SI);
+
         Changed = true;
         break;
       }

Modified: llvm/trunk/test/Transforms/InstCombine/select.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/InstCombine/select.ll?rev=123121&r1=123120&r2=123121&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/InstCombine/select.ll (original)
+++ llvm/trunk/test/Transforms/InstCombine/select.ll Sun Jan  9 10:00:11 2011
@@ -678,3 +678,14 @@
 ; CHECK-NEXT: %min = select i1 %is_a_nonpositive, i64 %a_ext, i64 2
 ; CHECK-NEXT: ret i64 %min
 }
+define i64 @test50(i32 %a) nounwind {
+	%is_a_nonpositive = icmp ult i32 %a, 3
+	%a_ext = sext i32 %a to i64
+	%min = select i1 %is_a_nonpositive, i64 2, i64 %a_ext
+	ret i64 %min
+; CHECK: @test50
+; CHECK-NEXT: %a_ext = sext i32 %a to i64
+; CHECK-NEXT: %is_a_nonpositive = icmp ugt i64 %a_ext, 2
+; CHECK-NEXT: %min = select i1 %is_a_nonpositive, i64 %a_ext, i64 2
+; CHECK-NEXT: ret i64 %min
+}