[llvm-commits] [llvm] r52259 - in /llvm/trunk: lib/Transforms/Scalar/InstructionCombining.cpp test/Transforms/InstCombine/2008-06-13-ReadOnlyCallStore.ll

[Eli Friedman]

Author: efriedma
Date: Fri Jun 13 17:02:12 2008
New Revision: 52259

URL: http://llvm.org/viewvc/llvm-project?rev=52259&view=rev
Log:
Don't skip over instructions other than loads that might read memory 
when trying to sink stores.


Added:
    llvm/trunk/test/Transforms/InstCombine/2008-06-13-ReadOnlyCallStore.ll
Modified:
    llvm/trunk/lib/Transforms/Scalar/InstructionCombining.cpp

Modified: llvm/trunk/lib/Transforms/Scalar/InstructionCombining.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Scalar/InstructionCombining.cpp?rev=52259&r1=52258&r2=52259&view=diff

==============================================================================
--- llvm/trunk/lib/Transforms/Scalar/InstructionCombining.cpp (original)
+++ llvm/trunk/lib/Transforms/Scalar/InstructionCombining.cpp Fri Jun 13 17:02:12 2008
@@ -10417,18 +10417,19 @@
           return false;
         break;
       }
-      // If we find something that may be using the stored value, or if we run
-      // out of instructions, we can't do the xform.
-      if (isa<LoadInst>(BBI) || BBI->mayWriteToMemory() ||
+      // If we find something that may be using or overwriting the stored
+      // value, or if we run out of instructions, we can't do the xform.
+      if (BBI->mayReadFromMemory() || BBI->mayWriteToMemory() ||
           BBI == OtherBB->begin())
         return false;
     }
     
     // In order to eliminate the store in OtherBr, we have to
-    // make sure nothing reads the stored value in StoreBB.
+    // make sure nothing reads or overwrites the stored value in
+    // StoreBB.
     for (BasicBlock::iterator I = StoreBB->begin(); &*I != &SI; ++I) {
       // FIXME: This should really be AA driven.
-      if (isa<LoadInst>(I) || I->mayWriteToMemory())
+      if (I->mayReadFromMemory() || I->mayWriteToMemory())
         return false;
     }
   }

Added: llvm/trunk/test/Transforms/InstCombine/2008-06-13-ReadOnlyCallStore.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/InstCombine/2008-06-13-ReadOnlyCallStore.ll?rev=52259&view=auto

==============================================================================
--- llvm/trunk/test/Transforms/InstCombine/2008-06-13-ReadOnlyCallStore.ll (added)
+++ llvm/trunk/test/Transforms/InstCombine/2008-06-13-ReadOnlyCallStore.ll Fri Jun 13 17:02:12 2008
@@ -0,0 +1,19 @@
+; RUN: llvm-as < %s | opt -instcombine | llvm-dis | grep {store i8} | count 2
+
+define i32 @a(i8* %s) nounwind  {
+entry:
+	store i8 0, i8* %s, align 1 ; This store cannot be eliminated!
+	%tmp3 = call i32 @strlen( i8* %s ) nounwind readonly
+	%tmp5 = icmp ne i32 %tmp3, 0
+	br i1 %tmp5, label %bb, label %bb8
+
+bb:		; preds = %entry
+	store i8 0, i8* %s, align 1
+	br label %bb8
+
+bb8:
+	ret i32 %tmp3
+}
+
+declare i32 @strlen(i8*) nounwind readonly 
+