[CVP] simplify phi with constant incoming values that match common variable edge values

This is based on an example that was recently posted on llvm-dev:

void *propagate_null(void* b, int* g) {
  if (!b) {
    return 0;
  }
  (*g)++;
  return b;
}

https://godbolt.org/g/xYk3qG

The original code or constant propagation in other passes has obscured the fact 
that the phi can be removed completely.

Differential Revision: https://reviews.llvm.org/D45448

llvm-svn: 329755

1 files changed, 94 insertions, 0 deletions

diff --git a/llvm/test/Transforms/CorrelatedValuePropagation/phi-common-val.ll b/llvm/test/Transforms/CorrelatedValuePropagation/phi-common-val.ll
new file mode 100644
index 00000000000..3011fef9749
--- /dev/null
+++ b/llvm/test/Transforms/CorrelatedValuePropagation/phi-common-val.ll
@@ -0,0 +1,94 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; RUN: opt < %s -correlated-propagation -S | FileCheck %s
+
+define i8* @simplify_phi_common_value_op0(i8* %ptr, i32* %b) {
+; CHECK-LABEL: @simplify_phi_common_value_op0(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    [[ISNULL:%.*]] = icmp eq i8* [[PTR:%.*]], null
+; CHECK-NEXT:    br i1 [[ISNULL]], label [[RETURN:%.*]], label [[ELSE:%.*]]
+; CHECK:       else:
+; CHECK-NEXT:    [[LB:%.*]] = load i32, i32* [[B:%.*]]
+; CHECK-NEXT:    [[ADD:%.*]] = add nsw i32 [[LB]], 1
+; CHECK-NEXT:    store i32 [[ADD]], i32* [[B]]
+; CHECK-NEXT:    br label [[RETURN]]
+; CHECK:       return:
+; CHECK-NEXT:    ret i8* [[PTR]]
+;
+entry:
+  %isnull = icmp eq i8* %ptr, null
+  br i1 %isnull, label %return, label %else
+
+else:
+  %lb = load i32, i32* %b
+  %add = add nsw i32 %lb, 1
+  store i32 %add, i32* %b
+  br label %return
+
+return:
+  %r = phi i8* [ %ptr, %else ], [ null, %entry ]
+  ret i8* %r
+}
+
+define i8* @simplify_phi_common_value_op1(i8* %ptr, i32* %b) {
+; CHECK-LABEL: @simplify_phi_common_value_op1(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    [[ISNULL:%.*]] = icmp eq i8* [[PTR:%.*]], null
+; CHECK-NEXT:    br i1 [[ISNULL]], label [[RETURN:%.*]], label [[ELSE:%.*]]
+; CHECK:       else:
+; CHECK-NEXT:    [[LB:%.*]] = load i32, i32* [[B:%.*]]
+; CHECK-NEXT:    [[ADD:%.*]] = add i32 [[LB]], 1
+; CHECK-NEXT:    store i32 [[ADD]], i32* [[B]]
+; CHECK-NEXT:    br label [[RETURN]]
+; CHECK:       return:
+; CHECK-NEXT:    ret i8* [[PTR]]
+;
+entry:
+  %isnull = icmp eq i8* %ptr, null
+  br i1 %isnull, label %return, label %else
+
+else:
+  %lb = load i32, i32* %b
+  %add = add i32 %lb, 1
+  store i32 %add, i32* %b
+  br label %return
+
+return:
+  %r = phi i8* [ null, %entry], [ %ptr, %else ]
+  ret i8* %r
+}
+
+define i8 @simplify_phi_multiple_constants(i8 %x, i32* %b) {
+; CHECK-LABEL: @simplify_phi_multiple_constants(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    [[IS0:%.*]] = icmp eq i8 [[X:%.*]], 0
+; CHECK-NEXT:    br i1 [[IS0]], label [[RETURN:%.*]], label [[ELSE1:%.*]]
+; CHECK:       else1:
+; CHECK-NEXT:    [[IS42:%.*]] = icmp eq i8 [[X]], 42
+; CHECK-NEXT:    br i1 [[IS42]], label [[RETURN]], label [[ELSE2:%.*]]
+; CHECK:       else2:
+; CHECK-NEXT:    [[LB:%.*]] = load i32, i32* [[B:%.*]]
+; CHECK-NEXT:    [[ADD:%.*]] = add i32 [[LB]], 1
+; CHECK-NEXT:    store i32 [[ADD]], i32* [[B]]
+; CHECK-NEXT:    br label [[RETURN]]
+; CHECK:       return:
+; CHECK-NEXT:    ret i8 [[X]]
+;
+entry:
+  %is0 = icmp eq i8 %x, 0
+  br i1 %is0, label %return, label %else1
+
+else1:
+  %is42 = icmp eq i8 %x, 42
+  br i1 %is42, label %return, label %else2
+
+else2:
+  %lb = load i32, i32* %b
+  %add = add i32 %lb, 1
+  store i32 %add, i32* %b
+  br label %return
+
+return:
+  %r = phi i8 [ 0, %entry], [ %x, %else2 ], [ 42, %else1 ]
+  ret i8 %r
+}
+