[llvm-commits] [llvm] r122164 - in /llvm/trunk: lib/Transforms/Scalar/CodeGenPrepare.cpp test/Transforms/CodeGenPrepare/basic.ll

[Chris Lattner]

Author: lattner
Date: Sat Dec 18 21:02:34 2010
New Revision: 122164

URL: http://llvm.org/viewvc/llvm-project?rev=122164&view=rev
Log:
first step to fixing PR8642: don't fold away empty basic blocks
which have trapping constant exprs in them due to PHI nodes.
Eliminating them can cause the constant expr to be evalutated
on new paths if the input edges are critical.


Added:
    llvm/trunk/test/Transforms/CodeGenPrepare/basic.ll
Modified:
    llvm/trunk/lib/Transforms/Scalar/CodeGenPrepare.cpp

Modified: llvm/trunk/lib/Transforms/Scalar/CodeGenPrepare.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Scalar/CodeGenPrepare.cpp?rev=122164&r1=122163&r2=122164&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/Scalar/CodeGenPrepare.cpp (original)
+++ llvm/trunk/lib/Transforms/Scalar/CodeGenPrepare.cpp Sat Dec 18 21:02:34 2010
@@ -211,6 +211,17 @@
   const PHINode *DestBBPN = dyn_cast<PHINode>(DestBB->begin());
   if (!DestBBPN) return true;  // no conflict.
 
+  // Walk all the PHI nodes in DestBB.  If any of the input values to the PHI
+  // are trapping constant exprs, then merging this block would introduce the
+  // possible trap into new control flow if we have any critical predecessor
+  // edges.
+  for (BasicBlock::const_iterator I = DestBB->begin(); isa<PHINode>(I); ++I) {
+    const PHINode *PN = cast<PHINode>(I);
+    if (const Constant *C =dyn_cast<Constant>(PN->getIncomingValueForBlock(BB)))
+      if (C->canTrap())
+        return false;
+  }
+  
   // Collect the preds of BB.
   SmallPtrSet<const BasicBlock*, 16> BBPreds;
   if (const PHINode *BBPN = dyn_cast<PHINode>(BB->begin())) {

Added: llvm/trunk/test/Transforms/CodeGenPrepare/basic.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/CodeGenPrepare/basic.ll?rev=122164&view=auto
==============================================================================
--- llvm/trunk/test/Transforms/CodeGenPrepare/basic.ll (added)
+++ llvm/trunk/test/Transforms/CodeGenPrepare/basic.ll Sat Dec 18 21:02:34 2010
@@ -0,0 +1,31 @@
+; RUN: opt -codegenprepare %s -S | FileCheck %s
+; PR8642
+
+%0 = type <{ %1, %1 }>
+%1 = type { i8, i8, i8, i8 }
+
+ at g_2 = global %0 <{ %1 { i8 1, i8 0, i8 0, i8 undef }, %1 { i8 2, i8 0, i8 0, i8 undef } }>, align 4
+ at g_4 = global %1 { i8 3, i8 0, i8 0, i8 undef }, align 4
+
+; CGP shouldn't fold away the empty cond.false.i block, because the constant
+; expr that will get dropped into it could trap.
+define i16 @test1(i8** %argv, i1 %c) nounwind ssp {
+entry:
+  br i1 %c, label %cond.end.i, label %cond.false.i
+
+cond.false.i:                                     ; preds = %entry
+  br label %foo.exit
+
+cond.end.i:                                       ; preds = %entry
+  store i8* null, i8** %argv
+  br label %foo.exit
+
+foo.exit:                                         ; preds = %cond.end.i, %cond.false.i
+  %call1 = phi i16 [ trunc (i32 srem (i32 1, i32 zext (i1 icmp eq (%1* bitcast (i8* getelementptr inbounds (%0* @g_2, i64 0, i32 1, i32 0) to %1*), %1* @g_4) to i32)) to i16), %cond.false.i ], [ 1, %cond.end.i ]
+  ret i16 %call1
+  
+; CHECK: @test1
+; CHECK: cond.false.i:
+; CHECK-NEXT:  br label %foo.exit
+}
+