[InstCombine] Revert r238452: Fold IntToPtr and PtrToInt into preceding loads.

According to git bisect, this is the root cause of a miscompile for Regex in
libLLVMSupport. I am still working on reducing a test case.
The actual bug may be elsewhere and this commit just exposed it.

Anyway, at the moment, to reproduce, follow these steps:
1. Build clang and libLTO in release mode.
2. Create a new build directory <stage2> and cd into it.
3. Use clang and libLTO from #1 to build llvm-extract in Release mode + asserts
   using -O2 -flto
4. Run llvm-extract  -ralias '.*bar' -S test/Other/extract-alias.ll

Result:
program doesn't contain global named '.*bar'!

Expected result:
@a0a0bar = alias void ()* @bar
@a0bar = alias void ()* @bar

declare void @bar()

Note: In step #3, if you don't use lto or asserts, the miscompile disappears.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@259674 91177308-0d34-0410-b5e6-96231b3b80d8

Author: Quentin Colombet

lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp

@@ -495,17 +495,12 @@ static Instruction *combineLoadToOperationType(InstCombiner &IC, LoadInst &LI) {
   }
 
   // Fold away bit casts of the loaded value by loading the desired type.
-  // We can do this for BitCastInsts as well as casts from and to pointer types,
-  // as long as those are noops (i.e., the source or dest type have the same
-  // bitwidth as the target's pointers).
   if (LI.hasOneUse())
-    if (auto* CI = dyn_cast<CastInst>(LI.user_back())) {
-      if (CI->isNoopCast(DL)) {
-        LoadInst *NewLoad = combineLoadToNewType(IC, LI, CI->getDestTy());
-        CI->replaceAllUsesWith(NewLoad);
-        IC.eraseInstFromFunction(*CI);
-        return &LI;
-      }
+    if (auto *BC = dyn_cast<BitCastInst>(LI.user_back())) {
+      LoadInst *NewLoad = combineLoadToNewType(IC, LI, BC->getDestTy());
+      BC->replaceAllUsesWith(NewLoad);
+      IC.eraseInstFromFunction(*BC);
+      return &LI;
     }
 
   // FIXME: We should also canonicalize loads of vectors when their elements are

test/Transforms/InstCombine/load-bitcast32.ll

@@ -72,14 +72,14 @@ entry:
   %yo107 = call i64 @llvm.objectsize.i64.p0i8(i8* %b, i1 false)
   %call50 = call i8* @__memmove_chk(i8* %b, i8* %a, i64 %add180, i64 %yo107)
 ; CHECK: %strlen = call i64 @strlen(i8* %b)
-; CHECK-NEXT: %strchr2 = getelementptr i8, i8* %b, i64 %strlen
+; CHECK-NEXT: [[STRCHR:%[0-9a-zA-Z_-]+]] = getelementptr i8, i8* %b, i64 %strlen
   %call51i = call i8* @strrchr(i8* %b, i32 0)
   %d = load i8*, i8** %c, align 8
   %sub182 = ptrtoint i8* %d to i64
   %sub183 = ptrtoint i8* %b to i64
   %sub184 = sub i64 %sub182, %sub183
   %add52.i.i = add nsw i64 %sub184, 1
-; CHECK: call void @llvm.memset.p0i8.i64(i8* %strchr2
+; CHECK: call void @llvm.memset.p0i8.i64(i8* [[STRCHR]]
   %call185 = call i8* @__memset_chk(i8* %call51i, i32 0, i64 %add52.i.i, i64 -1)
   ret i32 4
 }