[PATCH] D14596: [SROA] Choose more profitable type in findCommonType

[Guozhi Wei via llvm-commits]

Carrot updated this revision to Diff 50887.
Carrot added a comment.

This updated patch fixed https://llvm.org/bugs/show_bug.cgi?id=26918.

The problem of the reverted patch is when we have following code

; <label>:2:                                      ; preds = %0

  %3 = load atomic i64, i64* %1 monotonic, align 8
  br label %8

; <label>:4:                                      ; preds = %0, %0

  %5 = load atomic i64, i64* %1 acquire, align 8
  br label %8

; <label>:6:                                      ; preds = %0

  %7 = load atomic i64, i64* %1 seq_cst, align 8
  br label %8

; <label>:8:                                      ; preds = %6, %4, %2

  %.in1097491 = phi i64 [ %3, %2 ], [ %7, %6 ], [ %5, %4 ]
  %9 = bitcast i64 %.in1097491 to double
  ret double %9

My patch changed it to

; <label>:2:                                      ; preds = %0

  %3 = load atomic i64, i64* %1 monotonic, align 8
  %4 = bitcast i64 %3 to double
  br label %11

; <label>:5:                                      ; preds = %0, %0

  %6 = load atomic i64, i64* %1 acquire, align 8
  %7 = bitcast i64 %6 to double
  br label %11

; <label>:8:                                      ; preds = %0

  %9 = load atomic i64, i64* %1 seq_cst, align 8
  %10 = bitcast i64 %9 to double
  br label %11

; <label>:11:                                     ; preds = %8, %5, %2

  %12 = phi double [ %4, %2 ], [ %10, %8 ], [ %7, %5 ]
  %.in1097491 = phi i64 [ %3, %2 ], [ %9, %8 ], [ %6, %5 ]
  ret double %12

And expects ld/st combining can combine the load instructions with following bitcast. But ld/st combining doesn't change volatile/atomic memory access, so the bitcast instructions are left there. Later phi combining transformed it back to the original form, so the two combining transforms the code back and forth indefinitely.

There are two changes compared to the original approved patch:

  1 avoid changing volatile/atomic memory access
  2 add the impacted instructions to combining worklist

Please take another look.


http://reviews.llvm.org/D14596

Files:
  lib/Transforms/InstCombine/InstCombineCasts.cpp
  lib/Transforms/InstCombine/InstCombineInternal.h
  test/Transforms/InstCombine/pr25342.ll

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