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llvm-mirror/test/CodeGen/AArch64/load-combine-big-endian.ll
Artur Pilipenko 0e6418640a [DAGCombiner] Match load by bytes idiom and fold it into a single load. Attempt #2. 
The previous patch (https://reviews.llvm.org/rL289538) got reverted because of a bug. Chandler also requested some changes to the algorithm.
http://lists.llvm.org/pipermail/llvm-commits/Week-of-Mon-20161212/413479.html

This is an updated patch. The key difference is that collectBitProviders (renamed to calculateByteProvider) now collects the origin of one byte, not the whole value. It simplifies the implementation and allows to stop the traversal earlier if we know that the result won't be used.

From the original commit:

Match a pattern where a wide type scalar value is loaded by several narrow loads and combined by shifts and ors. Fold it into a single load or a load and a bswap if the targets supports it.

Assuming little endian target:
  i8 *a = ...
  i32 val = a[0] | (a[1] << 8) | (a[2] << 16) | (a[3] << 24)
=>
  i32 val = *((i32)a)

  i8 *a = ...
  i32 val = (a[0] << 24) | (a[1] << 16) | (a[2] << 8) | a[3]
=>
  i32 val = BSWAP(*((i32)a))

This optimization was discussed on llvm-dev some time ago in "Load combine pass" thread. We came to the conclusion that we want to do this transformation late in the pipeline because in presence of atomic loads load widening is irreversible transformation and it might hinder other optimizations.

Eventually we'd like to support folding patterns like this where the offset has a variable and a constant part:
  i32 val = a[i] | (a[i + 1] << 8) | (a[i + 2] << 16) | (a[i + 3] << 24)

Matching the pattern above is easier at SelectionDAG level since address reassociation has already happened and the fact that the loads are adjacent is clear. Understanding that these loads are adjacent at IR level would have involved looking through geps/zexts/adds while looking at the addresses.

The general scheme is to match OR expressions by recursively calculating the origin of individual bytes which constitute the resulting OR value. If all the OR bytes come from memory verify that they are adjacent and match with little or big endian encoding of a wider value. If so and the load of the wider type (and bswap if needed) is allowed by the target generate a load and a bswap if needed.

Reviewed By: RKSimon, filcab, chandlerc 

Differential Revision: https://reviews.llvm.org/D27861

llvm-svn: 293036
2017-01-25 08:53:31 +00:00

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; RUN: llc < %s -mtriple=arm64eb-unknown | FileCheck %s
; i8* p; // p is 4 byte aligned
; ((i32) p[0] << 24) | ((i32) p[1] << 16) | ((i32) p[2] << 8) | (i32) p[3]
define i32 @load_i32_by_i8_big_endian(i32* %arg) {
; CHECK-LABEL: load_i32_by_i8_big_endian:
; CHECK: ldr w0, [x0]
; CHECK-NEXT: ret
%tmp = bitcast i32* %arg to i8*
%tmp1 = load i8, i8* %tmp, align 4
%tmp2 = zext i8 %tmp1 to i32
%tmp3 = shl nuw nsw i32 %tmp2, 24
%tmp4 = getelementptr inbounds i8, i8* %tmp, i32 1
%tmp5 = load i8, i8* %tmp4, align 1
%tmp6 = zext i8 %tmp5 to i32
%tmp7 = shl nuw nsw i32 %tmp6, 16
%tmp8 = or i32 %tmp7, %tmp3
%tmp9 = getelementptr inbounds i8, i8* %tmp, i32 2
%tmp10 = load i8, i8* %tmp9, align 1
%tmp11 = zext i8 %tmp10 to i32
%tmp12 = shl nuw nsw i32 %tmp11, 8
%tmp13 = or i32 %tmp8, %tmp12
%tmp14 = getelementptr inbounds i8, i8* %tmp, i32 3
%tmp15 = load i8, i8* %tmp14, align 1
%tmp16 = zext i8 %tmp15 to i32
%tmp17 = or i32 %tmp13, %tmp16
ret i32 %tmp17
}
; i8* p; // p is 4 byte aligned
; ((i32) (((i16) p[0] << 8) | (i16) p[1]) << 16) | (i32) (((i16) p[3] << 8) | (i16) p[4])
define i32 @load_i32_by_i16_by_i8_big_endian(i32* %arg) {
; CHECK-LABEL: load_i32_by_i16_by_i8_big_endian:
; CHECK: ldr w0, [x0]
; CHECK-NEXT: ret
%tmp = bitcast i32* %arg to i8*
%tmp1 = load i8, i8* %tmp, align 4
%tmp2 = zext i8 %tmp1 to i16
%tmp3 = getelementptr inbounds i8, i8* %tmp, i32 1
%tmp4 = load i8, i8* %tmp3, align 1
%tmp5 = zext i8 %tmp4 to i16
%tmp6 = shl nuw nsw i16 %tmp2, 8
%tmp7 = or i16 %tmp6, %tmp5
%tmp8 = getelementptr inbounds i8, i8* %tmp, i32 2
%tmp9 = load i8, i8* %tmp8, align 1
%tmp10 = zext i8 %tmp9 to i16
%tmp11 = getelementptr inbounds i8, i8* %tmp, i32 3
%tmp12 = load i8, i8* %tmp11, align 1
%tmp13 = zext i8 %tmp12 to i16
%tmp14 = shl nuw nsw i16 %tmp10, 8
%tmp15 = or i16 %tmp14, %tmp13
%tmp16 = zext i16 %tmp7 to i32
%tmp17 = zext i16 %tmp15 to i32
%tmp18 = shl nuw nsw i32 %tmp16, 16
%tmp19 = or i32 %tmp18, %tmp17
ret i32 %tmp19
}
; i16* p; // p is 4 byte aligned
; ((i32) p[0] << 16) | (i32) p[1]
define i32 @load_i32_by_i16(i32* %arg) {
; CHECK-LABEL: load_i32_by_i16:
; CHECK: ldr w0, [x0]
; CHECK-NEXT: ret
%tmp = bitcast i32* %arg to i16*
%tmp1 = load i16, i16* %tmp, align 4
%tmp2 = zext i16 %tmp1 to i32
%tmp3 = getelementptr inbounds i16, i16* %tmp, i32 1
%tmp4 = load i16, i16* %tmp3, align 1
%tmp5 = zext i16 %tmp4 to i32
%tmp6 = shl nuw nsw i32 %tmp2, 16
%tmp7 = or i32 %tmp6, %tmp5
ret i32 %tmp7
}
; i16* p_16; // p_16 is 4 byte aligned
; i8* p_8 = (i8*) p_16;
; (i32) (p_16[0] << 16) | ((i32) p[2] << 8) | (i32) p[3]
define i32 @load_i32_by_i16_i8(i32* %arg) {
; CHECK-LABEL: load_i32_by_i16_i8:
; CHECK: ldr w0, [x0]
; CHECK-NEXT: ret
%tmp = bitcast i32* %arg to i16*
%tmp1 = bitcast i32* %arg to i8*
%tmp2 = load i16, i16* %tmp, align 4
%tmp3 = zext i16 %tmp2 to i32
%tmp4 = shl nuw nsw i32 %tmp3, 16
%tmp5 = getelementptr inbounds i8, i8* %tmp1, i32 2
%tmp6 = load i8, i8* %tmp5, align 1
%tmp7 = zext i8 %tmp6 to i32
%tmp8 = shl nuw nsw i32 %tmp7, 8
%tmp9 = getelementptr inbounds i8, i8* %tmp1, i32 3
%tmp10 = load i8, i8* %tmp9, align 1
%tmp11 = zext i8 %tmp10 to i32
%tmp12 = or i32 %tmp8, %tmp11
%tmp13 = or i32 %tmp12, %tmp4
ret i32 %tmp13
}
; i8* p; // p is 8 byte aligned
; (i64) p[0] | ((i64) p[1] << 8) | ((i64) p[2] << 16) | ((i64) p[3] << 24) | ((i64) p[4] << 32) | ((i64) p[5] << 40) | ((i64) p[6] << 48) | ((i64) p[7] << 56)
define i64 @load_i64_by_i8_bswap(i64* %arg) {
; CHECK-LABEL: load_i64_by_i8_bswap:
; CHECK: ldr x8, [x0]
; CHECK-NEXT: rev x0, x8
; CHECK-NEXT: ret
%tmp = bitcast i64* %arg to i8*
%tmp1 = load i8, i8* %tmp, align 8
%tmp2 = zext i8 %tmp1 to i64
%tmp3 = getelementptr inbounds i8, i8* %tmp, i64 1
%tmp4 = load i8, i8* %tmp3, align 1
%tmp5 = zext i8 %tmp4 to i64
%tmp6 = shl nuw nsw i64 %tmp5, 8
%tmp7 = or i64 %tmp6, %tmp2
%tmp8 = getelementptr inbounds i8, i8* %tmp, i64 2
%tmp9 = load i8, i8* %tmp8, align 1
%tmp10 = zext i8 %tmp9 to i64
%tmp11 = shl nuw nsw i64 %tmp10, 16
%tmp12 = or i64 %tmp7, %tmp11
%tmp13 = getelementptr inbounds i8, i8* %tmp, i64 3
%tmp14 = load i8, i8* %tmp13, align 1
%tmp15 = zext i8 %tmp14 to i64
%tmp16 = shl nuw nsw i64 %tmp15, 24
%tmp17 = or i64 %tmp12, %tmp16
%tmp18 = getelementptr inbounds i8, i8* %tmp, i64 4
%tmp19 = load i8, i8* %tmp18, align 1
%tmp20 = zext i8 %tmp19 to i64
%tmp21 = shl nuw nsw i64 %tmp20, 32
%tmp22 = or i64 %tmp17, %tmp21
%tmp23 = getelementptr inbounds i8, i8* %tmp, i64 5
%tmp24 = load i8, i8* %tmp23, align 1
%tmp25 = zext i8 %tmp24 to i64
%tmp26 = shl nuw nsw i64 %tmp25, 40
%tmp27 = or i64 %tmp22, %tmp26
%tmp28 = getelementptr inbounds i8, i8* %tmp, i64 6
%tmp29 = load i8, i8* %tmp28, align 1
%tmp30 = zext i8 %tmp29 to i64
%tmp31 = shl nuw nsw i64 %tmp30, 48
%tmp32 = or i64 %tmp27, %tmp31
%tmp33 = getelementptr inbounds i8, i8* %tmp, i64 7
%tmp34 = load i8, i8* %tmp33, align 1
%tmp35 = zext i8 %tmp34 to i64
%tmp36 = shl nuw i64 %tmp35, 56
%tmp37 = or i64 %tmp32, %tmp36
ret i64 %tmp37
}
; i8* p; // p is 8 byte aligned
; ((i64) p[0] << 56) | ((i64) p[1] << 48) | ((i64) p[2] << 40) | ((i64) p[3] << 32) | ((i64) p[4] << 24) | ((i64) p[5] << 16) | ((i64) p[6] << 8) | (i64) p[7]
define i64 @load_i64_by_i8(i64* %arg) {
; CHECK-LABEL: load_i64_by_i8:
; CHECK: ldr x0, [x0]
; CHECK-NEXT: ret
%tmp = bitcast i64* %arg to i8*
%tmp1 = load i8, i8* %tmp, align 8
%tmp2 = zext i8 %tmp1 to i64
%tmp3 = shl nuw i64 %tmp2, 56
%tmp4 = getelementptr inbounds i8, i8* %tmp, i64 1
%tmp5 = load i8, i8* %tmp4, align 1
%tmp6 = zext i8 %tmp5 to i64
%tmp7 = shl nuw nsw i64 %tmp6, 48
%tmp8 = or i64 %tmp7, %tmp3
%tmp9 = getelementptr inbounds i8, i8* %tmp, i64 2
%tmp10 = load i8, i8* %tmp9, align 1
%tmp11 = zext i8 %tmp10 to i64
%tmp12 = shl nuw nsw i64 %tmp11, 40
%tmp13 = or i64 %tmp8, %tmp12
%tmp14 = getelementptr inbounds i8, i8* %tmp, i64 3
%tmp15 = load i8, i8* %tmp14, align 1
%tmp16 = zext i8 %tmp15 to i64
%tmp17 = shl nuw nsw i64 %tmp16, 32
%tmp18 = or i64 %tmp13, %tmp17
%tmp19 = getelementptr inbounds i8, i8* %tmp, i64 4
%tmp20 = load i8, i8* %tmp19, align 1
%tmp21 = zext i8 %tmp20 to i64
%tmp22 = shl nuw nsw i64 %tmp21, 24
%tmp23 = or i64 %tmp18, %tmp22
%tmp24 = getelementptr inbounds i8, i8* %tmp, i64 5
%tmp25 = load i8, i8* %tmp24, align 1
%tmp26 = zext i8 %tmp25 to i64
%tmp27 = shl nuw nsw i64 %tmp26, 16
%tmp28 = or i64 %tmp23, %tmp27
%tmp29 = getelementptr inbounds i8, i8* %tmp, i64 6
%tmp30 = load i8, i8* %tmp29, align 1
%tmp31 = zext i8 %tmp30 to i64
%tmp32 = shl nuw nsw i64 %tmp31, 8
%tmp33 = or i64 %tmp28, %tmp32
%tmp34 = getelementptr inbounds i8, i8* %tmp, i64 7
%tmp35 = load i8, i8* %tmp34, align 1
%tmp36 = zext i8 %tmp35 to i64
%tmp37 = or i64 %tmp33, %tmp36
ret i64 %tmp37
}
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