[PATCH] D28742: [InstCombine] Don't DSE across readnone functions that may throw

[Sanjoy Das via Phabricator via llvm-commits]

sanjoy created this revision.
sanjoy added reviewers: dberlin, chandlerc, hfinkel, majnemer.
sanjoy added a subscriber: llvm-commits.
sanjoy added a dependency: D28740: [LangRef] Explicitly allow readnone and reaodnly functions to unwind.
Herald added a subscriber: mcrosier.

Depends on https://reviews.llvm.org/D28740


https://reviews.llvm.org/D28742

Files:
  lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp
  test/Transforms/InstCombine/readnone-maythrow.ll


Index: test/Transforms/InstCombine/readnone-maythrow.ll
===================================================================
--- /dev/null
+++ test/Transforms/InstCombine/readnone-maythrow.ll
@@ -0,0 +1,34 @@
+; RUN: opt -S -instcombine < %s | FileCheck %s
+
+declare void @readnone_but_may_throw() readnone
+
+define void @f_0(i32* %ptr) {
+; CHECK-LABEL: @f_0(
+entry:
+; CHECK:  store i32 10, i32* %ptr
+; CHECK-NEXT:  call void @readnone_but_may_throw()
+; CHECK-NEXT:  store i32 20, i32* %ptr, align 4
+; CHECK:  ret void
+
+  store i32 10, i32* %ptr
+  call void @readnone_but_may_throw()
+  store i32 20, i32* %ptr
+  ret void
+}
+
+define void @f_1(i1 %cond, i32* %ptr) {
+; CHECK-LABEL: @f_1(
+; CHECK:  store i32 10, i32* %ptr
+; CHECK-NEXT:  call void @readnone_but_may_throw()
+
+  store i32 10, i32* %ptr
+  call void @readnone_but_may_throw()
+  br i1 %cond, label %left, label %merge
+
+left:
+  store i32 20, i32* %ptr
+  br label %merge
+
+merge:
+  ret void
+}
Index: lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp
===================================================================
--- lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp
+++ lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp
@@ -1267,8 +1267,8 @@
       break;
     }
 
-    // Don't skip over loads or things that can modify memory.
-    if (BBI->mayWriteToMemory() || BBI->mayReadFromMemory())
+    // Don't skip over loads, throws or things that can modify memory.
+    if (BBI->mayWriteToMemory() || BBI->mayReadFromMemoryOrThrow())
       break;
   }
 
@@ -1391,7 +1391,7 @@
       }
       // 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() ||
+      if (BBI->mayReadFromMemoryOrThrow() || BBI->mayWriteToMemory() ||
           BBI == OtherBB->begin())
         return false;
     }
@@ -1401,7 +1401,7 @@
     // StoreBB.
     for (BasicBlock::iterator I = StoreBB->begin(); &*I != &SI; ++I) {
       // FIXME: This should really be AA driven.
-      if (I->mayReadFromMemory() || I->mayWriteToMemory())
+      if (I->mayReadFromMemoryOrThrow() || I->mayWriteToMemory())
         return false;
     }
   }


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