LoopLoadElim: Respect convergent

[Meinersbur]

LGTM

[arsenm]

r363162

lib/Transforms/Scalar/LoopLoadElimination.cpp

bool processLoop() {
 
     if (LAI.getPSE().getUnionPredicate().getComplexity() >
         LoadElimSCEVCheckThreshold) {
       LLVM_DEBUG(dbgs() << "Too many SCEV run-time checks needed.\n");
       return false;
     }
 
     if (!Checks.empty() || !LAI.getPSE().getUnionPredicate().isAlwaysTrue()) {
+      if (LAI.hasConvergentOp()) {
+        LLVM_DEBUG(dbgs() << "Versioning is needed but not allowed with "
+                             "convergent calls\n");
+        return false;
+      }
+
       auto *HeaderBB = L->getHeader();
       auto *F = HeaderBB->getParent();
       bool OptForSize = F->hasOptSize() ||
                         llvm::shouldOptimizeForSize(HeaderBB, PSI, BFI);
       if (OptForSize) {
         LLVM_DEBUG(
             dbgs() << "Versioning is needed but not allowed when optimizing "
                       "for size.\n");

test/Transforms/LoopLoadElim/convergent.ll

+; RUN: opt -loop-load-elim -S < %s | FileCheck %s
+; RUN: opt -passes=loop-load-elim -S < %s | FileCheck %s
+
+; Simple st->ld forwarding derived from a lexical forward dep, but
+; can't introduce runtime checks with a convergent call.
+;
+;   for (unsigned i = 0; i < 100; i++) {
+;     A[i+1] = convergent(B[i]) + 2;
+;     C[i] = A[i] * 2;
+;   }
+
+target datalayout = "e-m:o-i64:64-f80:128-n8:16:32:64-S128"
+
+; CHECK-LABEL: @f_convergent(
+; CHECK: call i32 @llvm.convergent(
+; CHECK-NOT: call i32 @llvm.convergent(
+define void @f_convergent(i32* %A, i32* %B, i32* %C, i64 %N) #0 {
+
+entry:
+  br label %for.body
+
+for.body:                                         ; preds = %for.body, %entry
+  %indvars.iv = phi i64 [ 0, %entry ], [ %indvars.iv.next, %for.body ]
+  %indvars.iv.next = add nuw nsw i64 %indvars.iv, 1
+
+  %Aidx_next = getelementptr inbounds i32, i32* %A, i64 %indvars.iv.next
+  %Bidx = getelementptr inbounds i32, i32* %B, i64 %indvars.iv
+  %Cidx = getelementptr inbounds i32, i32* %C, i64 %indvars.iv
+  %Aidx = getelementptr inbounds i32, i32* %A, i64 %indvars.iv
+
+  %b = load i32, i32* %Bidx, align 4
+  %convergent.b = call i32 @llvm.convergent(i32 %b)
+
+  %a_p1 = add i32 %convergent.b, 2
+  store i32 %a_p1, i32* %Aidx_next, align 4
+
+  %a = load i32, i32* %Aidx, align 1
+  %c = mul i32 %a, 2
+  store i32 %c, i32* %Cidx, align 4
+
+  %exitcond = icmp eq i64 %indvars.iv.next, %N
+  br i1 %exitcond, label %for.end, label %for.body
+
+for.end:                                          ; preds = %for.body
+  ret void
+}
+
+declare i32 @llvm.convergent(i32) #1
+
+attributes #0 = { nounwind convergent }
+attributes #1 = { nounwind readnone convergent }