[llvm] r195118 - Fix an issue where SROA computed different results based on the relative

[Chandler Carruth]

Author: chandlerc
Date: Tue Nov 19 03:03:18 2013
New Revision: 195118

URL: http://llvm.org/viewvc/llvm-project?rev=195118&view=rev
Log:
Fix an issue where SROA computed different results based on the relative
order of slices of the alloca which have exactly the same size and other
properties. This was found by a perniciously unstable sort
implementation used to flush out buggy uses of the algorithm.

The fundamental idea is that findCommonType should return the best
common type it can find across all of the slices in the range. There
were two bugs here previously:

1) We would accept an integer type smaller than a byte-width multiple,
   and if there were different bit-width integer types, we would accept
   the first one. This caused an actual failure in the testcase updated
   here when the sort order changed.
2) If we found a bad combination of types or a non-load, non-store use
   before an integer typed load or store we would bail, but if we found
   the integere typed load or store, we would use it. The correct
   behavior is to always use an integer typed operation which covers the
   partition if one exists.

While a clever debugging sort algorithm found problem #1 in our existing
test cases, I have no useful test case ideas for #2. I spotted in by
inspection when looking at this code.

Modified:
    llvm/trunk/lib/Transforms/Scalar/SROA.cpp
    llvm/trunk/test/Transforms/SROA/basictest.ll

Modified: llvm/trunk/lib/Transforms/Scalar/SROA.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Scalar/SROA.cpp?rev=195118&r1=195117&r2=195118&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/Scalar/SROA.cpp (original)
+++ llvm/trunk/lib/Transforms/Scalar/SROA.cpp Tue Nov 19 03:03:18 2013
@@ -938,6 +938,7 @@ static Type *findCommonType(AllocaSlices
                             AllocaSlices::const_iterator E,
                             uint64_t EndOffset) {
   Type *Ty = 0;
+  bool IgnoreNonIntegralTypes = false;
   for (AllocaSlices::const_iterator I = B; I != E; ++I) {
     Use *U = I->getUse();
     if (isa<IntrinsicInst>(*U->getUser()))
@@ -946,29 +947,37 @@ static Type *findCommonType(AllocaSlices
       continue;
 
     Type *UserTy = 0;
-    if (LoadInst *LI = dyn_cast<LoadInst>(U->getUser()))
+    if (LoadInst *LI = dyn_cast<LoadInst>(U->getUser())) {
       UserTy = LI->getType();
-    else if (StoreInst *SI = dyn_cast<StoreInst>(U->getUser()))
+    } else if (StoreInst *SI = dyn_cast<StoreInst>(U->getUser())) {
       UserTy = SI->getValueOperand()->getType();
-    else
-      return 0; // Bail if we have weird uses.
+    } else {
+      IgnoreNonIntegralTypes = true; // Give up on anything but an iN type.
+      continue;
+    }
 
     if (IntegerType *ITy = dyn_cast<IntegerType>(UserTy)) {
       // If the type is larger than the partition, skip it. We only encounter
       // this for split integer operations where we want to use the type of the
-      // entity causing the split.
-      if (ITy->getBitWidth() / 8 > (EndOffset - B->beginOffset()))
+      // entity causing the split. Also skip if the type is not a byte width
+      // multiple.
+      if (ITy->getBitWidth() % 8 != 0 ||
+          ITy->getBitWidth() / 8 > (EndOffset - B->beginOffset()))
         continue;
 
       // If we have found an integer type use covering the alloca, use that
-      // regardless of the other types, as integers are often used for a
-      // "bucket
-      // of bits" type.
+      // regardless of the other types, as integers are often used for
+      // a "bucket of bits" type.
+      //
+      // NB: This *must* be the only return from inside the loop so that the
+      // order of slices doesn't impact the computed type.
       return ITy;
+    } else if (IgnoreNonIntegralTypes) {
+      continue;
     }
 
     if (Ty && Ty != UserTy)
-      return 0;
+      IgnoreNonIntegralTypes = true; // Give up on anything but an iN type.
 
     Ty = UserTy;
   }

Modified: llvm/trunk/test/Transforms/SROA/basictest.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/SROA/basictest.ll?rev=195118&r1=195117&r2=195118&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/SROA/basictest.ll (original)
+++ llvm/trunk/test/Transforms/SROA/basictest.ll Tue Nov 19 03:03:18 2013
@@ -1181,7 +1181,6 @@ entry:
   store i1 %x, i1* %b.i1, align 8
   %b.i8 = bitcast <{ i1 }>* %b to i8*
   %foo = load i8* %b.i8, align 1
-; CHECK-NEXT: {{.*}} = zext i1 %x to i8
 ; CHECK-NEXT: %[[ext:.*]] = zext i1 %x to i8
 ; CHECK-NEXT: store i8 %[[ext]], i8* %[[a]], align 8
 ; CHECK-NEXT: {{.*}} = load i8* %[[a]], align 8