[PATCH] D46162: [PowerPC] Don't transform to CTR loop if the decrement branch instr. would end up in a different loop

[Nemanja Ivanovic via Phabricator via llvm-commits]

nemanjai updated this revision to Diff 144271.
nemanjai added a comment.

I've produced a test case that closely resembles the original CFG. Also updated the condition to hopefully address the valid point that @efriedma brought up.
Please let me know if this is sufficient.


Repository:
  rL LLVM

https://reviews.llvm.org/D46162

Files:
  lib/Target/PowerPC/PPCCTRLoops.cpp
  test/CodeGen/PowerPC/no-ctr-loop-if-exit-in-nested-loop.ll


Index: test/CodeGen/PowerPC/no-ctr-loop-if-exit-in-nested-loop.ll
===================================================================
--- test/CodeGen/PowerPC/no-ctr-loop-if-exit-in-nested-loop.ll
+++ test/CodeGen/PowerPC/no-ctr-loop-if-exit-in-nested-loop.ll
@@ -0,0 +1,67 @@
+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py
+; RUN: llc -mcpu=pwr8 -mtriple=powerpc64le-unknown-unknown \
+; RUN:   -verify-machineinstrs < %s | FileCheck %s
+define signext i32 @test(i32* noalias %PtrA, i32* noalias %PtrB, i32 signext %LenA, i32 signext %LenB) #0 {
+; CHECK-LABEL: test:
+; CHECK-NOT: mtctr
+; CHECK-NOT: bdnz
+; CHECK-NOT: bdz
+; CHECK:     blr
+entry:
+  br label %block2
+
+block2:                                           ; preds = %entry
+  br label %block3
+
+block3:                                           ; preds = %block8, %block2
+  %OuterInd.0 = phi i32 [ 0, %block2 ], [ %inc, %block8 ]
+  %InnerInd.0 = phi i32 [ 0, %block2 ], [ %inc1, %block8 ]
+  %inc = add nsw i32 %OuterInd.0, 1
+  br label %block4
+
+block4:                                           ; preds = %if.then4, %block3
+  %InnerInd.1 = phi i32 [ %InnerInd.0, %block3 ], [ %inc1, %if.then4 ]
+  %cmp = icmp sge i32 %inc, %LenA
+  br i1 %cmp, label %if.then, label %if.end
+
+if.then:                                          ; preds = %block4
+  %sub = sub nsw i32 %inc, 1
+  %idxprom = sext i32 %sub to i64
+  %arrayidx = getelementptr inbounds i32, i32* %PtrA, i64 %idxprom
+  %0 = load i32, i32* %arrayidx, align 4
+  ret i32 %0
+
+if.end:                                           ; preds = %block4
+  br label %block5
+
+block5:                                           ; preds = %if.end
+  %inc1 = add nsw i32 %InnerInd.1, 1
+  %idxprom2 = sext i32 %InnerInd.1 to i64
+  %arrayidx3 = getelementptr inbounds i32, i32* %PtrB, i64 %idxprom2
+  %1 = load i32, i32* %arrayidx3, align 4
+  %tobool = icmp ne i32 %1, 0
+  br i1 %tobool, label %if.then4, label %if.end9
+
+if.then4:                                         ; preds = %block5
+  %idxprom5 = sext i32 %inc to i64
+  %arrayidx6 = getelementptr inbounds i32, i32* %PtrA, i64 %idxprom5
+  %2 = load i32, i32* %arrayidx6, align 4
+  %idxprom7 = sext i32 %inc1 to i64
+  %arrayidx8 = getelementptr inbounds i32, i32* %PtrB, i64 %idxprom7
+  store i32 %2, i32* %arrayidx8, align 4
+  br label %block4
+
+if.end9:                                          ; preds = %block5
+  br label %block6
+
+block6:                                           ; preds = %if.end9
+  %idxprom10 = sext i32 %inc to i64
+  %arrayidx11 = getelementptr inbounds i32, i32* %PtrA, i64 %idxprom10
+  %3 = load i32, i32* %arrayidx11, align 4
+  %inc12 = add nsw i32 %3, 1
+  store i32 %inc12, i32* %arrayidx11, align 4
+  br label %block8
+
+block8:                                           ; preds = %block6
+  br label %block3
+}
Index: lib/Target/PowerPC/PPCCTRLoops.cpp
===================================================================
--- lib/Target/PowerPC/PPCCTRLoops.cpp
+++ lib/Target/PowerPC/PPCCTRLoops.cpp
@@ -572,6 +572,12 @@
     if (SE->getTypeSizeInBits(EC->getType()) > (TM->isPPC64() ? 64 : 32))
       continue;
 
+    // If this exiting block is contained in a nested loop, it is not eligible
+    // for insertion of the branch-and-decrement since the inner loop would
+    // end up messing up the value in the CTR.
+    if (LI->getLoopFor(*I) != L || !DT->dominates(L->getHeader(), *I))
+      continue;
+
     // We now have a loop-invariant count of loop iterations (which is not the
     // constant zero) for which we know that this loop will not exit via this
     // exisiting block.


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