Fix a problem I introduced in r187029 where we would over-eagerly

schedule an alloca for another iteration in SROA. This only showed up
with a mixture of promotable and unpromotable selects and phis. Added
a test case for this.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@187031 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Transforms/Scalar/SROA.cpp

@@ -2576,7 +2576,6 @@ private:
     // occurs.
     if (isSafePHIToSpeculate(PN, &DL)) {
       Pass.SpeculatablePHIs.insert(&PN);
-      Pass.Worklist.insert(&NewAI);
       IsUsedByRewrittenSpeculatableInstructions = true;
       return true;
     }
@@ -2606,7 +2605,6 @@ private:
     // speculation occurs.
     if (isSafeSelectToSpeculate(SI, &DL)) {
       Pass.SpeculatableSelects.insert(&SI);
-      Pass.Worklist.insert(&NewAI);
       IsUsedByRewrittenSpeculatableInstructions = true;
       return true;
     }
@@ -3090,10 +3088,18 @@ bool SROA::rewritePartition(AllocaInst &AI, AllocaSlices &S,
   if (Promotable && !Rewriter.isUsedByRewrittenSpeculatableInstructions()) {
     DEBUG(dbgs() << "  and queuing for promotion\n");
     PromotableAllocas.push_back(NewAI);
-  } else if (NewAI != &AI) {
+  } else if (NewAI != &AI ||
+             (Promotable &&
+              Rewriter.isUsedByRewrittenSpeculatableInstructions())) {
     // If we can't promote the alloca, iterate on it to check for new
     // refinements exposed by splitting the current alloca. Don't iterate on an
     // alloca which didn't actually change and didn't get promoted.
+    //
+    // Alternatively, if we could promote the alloca but have speculatable
+    // instructions then we will speculate them after finishing our processing
+    // of the original alloca. Mark the new one for re-visiting in the next
+    // iteration so the speculated operations can be rewritten.
+    //
     // FIXME: We should actually track whether the rewriter changed anything.
     Worklist.insert(NewAI);
   }

test/Transforms/SROA/phi-and-select.ll

@@ -346,6 +346,43 @@ exit:
   ret i32 %load
 }
 
+define i32 @test14(i1 %b1, i1 %b2, i32* %ptr) {
+; Check for problems when there are both selects and phis and one is
+; speculatable toward promotion but the other is not. That should block all of
+; the speculation.
+; CHECK-LABEL: @test14(
+; CHECK: alloca
+; CHECK: alloca
+; CHECK: select
+; CHECK: phi
+; CHECK: phi
+; CHECK: select
+; CHECK: ret i32
+
+entry:
+  %f = alloca i32
+  %g = alloca i32
+  store i32 0, i32* %f
+  store i32 0, i32* %g
+  %f.select = select i1 %b1, i32* %f, i32* %ptr
+  br i1 %b2, label %then, label %else
+
+then:
+  br label %exit
+
+else:
+  br label %exit
+
+exit:
+  %f.phi = phi i32* [ %f, %then ], [ %f.select, %else ]
+  %g.phi = phi i32* [ %g, %then ], [ %ptr, %else ]
+  %f.loaded = load i32* %f.phi
+  %g.select = select i1 %b1, i32* %g, i32* %g.phi
+  %g.loaded = load i32* %g.select
+  %result = add i32 %f.loaded, %g.loaded
+  ret i32 %result
+}
+
 define i32 @PR13905() {
 ; Check a pattern where we have a chain of dead phi nodes to ensure they are
 ; deleted and promotion can proceed.