[llvm-commits] [llvm] r96428 - in /llvm/trunk: lib/Transforms/Scalar/LoopStrengthReduce.cpp test/CodeGen/X86/lsr-overflow.ll

[Dan Gohman]

Author: djg
Date: Tue Feb 16 18:41:53 2010
New Revision: 96428

URL: http://llvm.org/viewvc/llvm-project?rev=96428&view=rev
Log:
Don't attempt to divide INT_MIN by -1; consider such cases to
have overflowed.

Added:
    llvm/trunk/test/CodeGen/X86/lsr-overflow.ll
Modified:
    llvm/trunk/lib/Transforms/Scalar/LoopStrengthReduce.cpp

Modified: llvm/trunk/lib/Transforms/Scalar/LoopStrengthReduce.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Scalar/LoopStrengthReduce.cpp?rev=96428&r1=96427&r2=96428&view=diff

==============================================================================
--- llvm/trunk/lib/Transforms/Scalar/LoopStrengthReduce.cpp (original)
+++ llvm/trunk/lib/Transforms/Scalar/LoopStrengthReduce.cpp Tue Feb 16 18:41:53 2010
@@ -2112,12 +2112,16 @@
     Formula F = Base;
 
     // Check that the multiplication doesn't overflow.
+    if (F.AM.BaseOffs == INT64_MIN && Factor == -1)
+      continue;
     F.AM.BaseOffs = (uint64_t)Base.AM.BaseOffs * Factor;
     if ((int64_t)F.AM.BaseOffs / Factor != Base.AM.BaseOffs)
       continue;
 
     // Check that multiplying with the use offset doesn't overflow.
     int64_t Offset = LU.MinOffset;
+    if (Offset == INT64_MIN && Factor == -1)
+      continue;
     Offset = (uint64_t)Offset * Factor;
     if ((int64_t)Offset / Factor != LU.MinOffset)
       continue;

Added: llvm/trunk/test/CodeGen/X86/lsr-overflow.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/CodeGen/X86/lsr-overflow.ll?rev=96428&view=auto

==============================================================================
--- llvm/trunk/test/CodeGen/X86/lsr-overflow.ll (added)
+++ llvm/trunk/test/CodeGen/X86/lsr-overflow.ll Tue Feb 16 18:41:53 2010
@@ -0,0 +1,26 @@
+; RUN: llc < %s -march=x86-64 | FileCheck %s
+
+; The comparison uses the pre-inc value, which could lead LSR to
+; try to compute -INT64_MIN.
+
+; CHECK: movabsq $-9223372036854775808, %rax ## imm = 0x8000000000000000
+; CHECK: cmpq  %rax, %rbx
+; CHECK: sete  %al
+
+declare i64 @bar()
+
+define i1 @foo() nounwind {
+entry:
+  br label %for.cond.i
+
+for.cond.i:
+  %indvar = phi i64 [ 0, %entry ], [ %indvar.next, %for.cond.i ]
+  %t = call i64 @bar()
+  %indvar.next = add i64 %indvar, 1
+  %s = icmp ne i64 %indvar.next, %t
+  br i1 %s, label %for.cond.i, label %__ABContainsLabel.exit
+
+__ABContainsLabel.exit:
+  %cmp = icmp eq i64 %indvar, 9223372036854775807
+  ret i1 %cmp
+}