[PATCH] D133426: [LICM][LSR] Address a couple of special cases involving NULL.

[Stefan Pintilie via Phabricator via llvm-commits]

stefanp updated this revision to Diff 459824.
stefanp added a comment.

Sorry that this took a few days.
Removed the code from LICM.
Added a test for the loop strength reduction. The test shows simpler code when
the guard for the NULL is added. However, there may be other tests where the
reverse is true.


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D133426/new/

https://reviews.llvm.org/D133426

Files:
  llvm/lib/Transforms/Scalar/LoopStrengthReduce.cpp
  llvm/test/Transforms/LoopStrengthReduce/Power/opaque-null-ptr.ll


Index: llvm/test/Transforms/LoopStrengthReduce/Power/opaque-null-ptr.ll
===================================================================
--- /dev/null
+++ llvm/test/Transforms/LoopStrengthReduce/Power/opaque-null-ptr.ll
@@ -0,0 +1,40 @@
+; RUN: llc -O3 -mtriple=powerpc64le-unknown-linux-gnu -mcpu=pwr8 \
+; RUN:   -stop-after=loop-reduce %s -o - | FileCheck %s
+
+ %0 = type <{ float }>
+
+define void @test(ptr %arg1, ptr %arg2, float %storeval) local_unnamed_addr {
+; CHECK-LABEL: test
+; CHECK:       bb175:
+; CHECK-NEXT:    %lsr.iv = phi i64 [ %lsr.iv.next, %bb175 ], [ 0, %bb ]
+; CHECK-NEXT:    %i176 = phi i64 [ %i237, %bb175 ], [ 1, %bb ]
+; CHECK-NEXT:    %i237 = add nuw nsw i64 %i176, 2
+; CHECK-NEXT:    %lsr.iv.next = add nuw nsw i64 %lsr.iv, 8
+; CHECK-NEXT:    %i238 = icmp slt i64 %i237, -1
+; CHECK-NEXT:    br i1 %i238, label %bb175, label %bb239
+
+bb:
+  %i21 = getelementptr [0 x float], ptr %arg2, i64 0, i64 -1
+  br label %bb175
+
+bb175:                                            ; preds = %bb175, %bb
+  %i176 = phi i64 [ %i237, %bb175 ], [ 1, %bb ]
+  %i177 = phi float [ %i198, %bb175 ], [ 0.000000e+00, %bb ]
+  %i184 = shl i64 %i176, 2
+  %i185 = getelementptr %0, ptr %i21, i64 %i176, i32 0
+  %i186 = load float, ptr %i185, align 4
+  %uglygep = getelementptr i8, ptr null, i64 %i184
+  %uglygep2 = getelementptr i8, ptr %uglygep, i64 4
+  %i190 = load float, ptr %uglygep2, align 4
+  %i193 = load float, ptr %uglygep, align 4
+  %i194 = fmul contract float %i186, %i193
+  %i195 = fadd contract float %i177, %i194
+  %i198 = fsub contract float %i195, %i190
+  %i237 = add nuw nsw i64 %i176, 2
+  %i238 = icmp slt i64 %i237, -1
+  br i1 %i238, label %bb175, label %bb239
+
+bb239:                                            ; preds = %bb175
+  store float %storeval, ptr null, align 4
+  ret void
+}
Index: llvm/lib/Transforms/Scalar/LoopStrengthReduce.cpp
===================================================================
--- llvm/lib/Transforms/Scalar/LoopStrengthReduce.cpp
+++ llvm/lib/Transforms/Scalar/LoopStrengthReduce.cpp
@@ -3471,9 +3471,14 @@
       if (const Instruction *Inst = dyn_cast<Instruction>(V)) {
         // Look for instructions defined outside the loop.
         if (L->contains(Inst)) continue;
-      } else if (isa<UndefValue>(V))
+      } else if (isa<UndefValue>(V)) {
         // Undef doesn't have a live range, so it doesn't matter.
         continue;
+      } else if (const Constant *Const = dyn_cast<Constant>(V)) {
+        // NULL values don't really have a live range. They are just NULL.
+        if (Const->isNullValue())
+          continue;
+      }
       for (const Use &U : V->uses()) {
         const Instruction *UserInst = dyn_cast<Instruction>(U.getUser());
         // Ignore non-instructions.


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