[DAGCombiner] Slice a big load in two loads when the element are next to each

other in memory and the target has paired load and performs post-isel loads
combining.

E.g., this optimization will transform something like this:
 a = load i64* addr
 b = trunc i64 a to i32
 c = lshr i64 a, 32
 d = trunc i64 c to i32

into:
 b = load i32* addr1
 d = load i32* addr2
Where addr1 = addr2 +/- sizeof(i32), if the target supports paired load and
performs post-isel loads combining.

One should overload TargetLowering::hasPairedLoad to provide this information.
The default is false.

<rdar://problem/14477220>


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@192471 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 140 insertions, 0 deletions

diff --git a/test/CodeGen/X86/load-slice.ll b/test/CodeGen/X86/load-slice.ll
new file mode 100644
index 0000000..83c7aa7
--- /dev/null
+++ b/test/CodeGen/X86/load-slice.ll
@@ -0,0 +1,140 @@
+; RUN: llc -mtriple x86_64-apple-macosx -combiner-stress-load-slicing < %s -o - | FileCheck %s --check-prefix=STRESS
+; RUN: llc -mtriple x86_64-apple-macosx < %s -o - | FileCheck %s --check-prefix=REGULAR
+;
+; <rdar://problem/14477220>
+
+%class.Complex = type { float, float }
+
+
+; Check that independant slices leads to independant loads then the slices leads to
+; different register file.
+;
+; The layout is:
+; LSB 0 1 2 3 | 4 5 6 7 MSB
+;       Low      High
+; The base address points to 0 and is 8-bytes aligned.
+; Low slice starts at 0 (base) and is 8-bytes aligned.
+; High slice starts at 4 (base + 4-bytes) and is 4-bytes aligned.
+;
+; STRESS-LABEL: t1:
+; Load out[out_start + 8].imm, this is base + 8 * 8 + 4.
+; STRESS: vmovss 68([[BASE:[^)]+]]), [[OUT_Imm:%xmm[0-9]+]]
+; Add high slice: out[out_start].imm, this is base + 4.
+; STRESS-NEXT: vaddss 4([[BASE]]), [[OUT_Imm]], [[RES_Imm:%xmm[0-9]+]]
+; Load out[out_start + 8].real, this is base + 8 * 8 + 0.
+; STRESS-NEXT: vmovss 64([[BASE]]), [[OUT_Real:%xmm[0-9]+]]
+; Add low slice: out[out_start].real, this is base + 0.
+; STRESS-NEXT: vaddss ([[BASE]]), [[OUT_Real]], [[RES_Real:%xmm[0-9]+]]
+; Swap Imm and Real.
+; STRESS-NEXT: vinsertps $16, [[RES_Imm]], [[RES_Real]], [[RES_Vec:%xmm[0-9]+]]
+; Put the results back into out[out_start].
+; STRESS-NEXT: vmovq [[RES_Vec]], ([[BASE]])
+;
+; Same for REGULAR, we eliminate register bank copy with each slices.
+; REGULAR-LABEL: t1:
+; Load out[out_start + 8].imm, this is base + 8 * 8 + 4.
+; REGULAR: vmovss 68([[BASE:[^)]+]]), [[OUT_Imm:%xmm[0-9]+]]
+; Add high slice: out[out_start].imm, this is base + 4.
+; REGULAR-NEXT: vaddss 4([[BASE]]), [[OUT_Imm]], [[RES_Imm:%xmm[0-9]+]]
+; Load out[out_start + 8].real, this is base + 8 * 8 + 0.
+; REGULAR-NEXT: vmovss 64([[BASE]]), [[OUT_Real:%xmm[0-9]+]]
+; Add low slice: out[out_start].real, this is base + 0.
+; REGULAR-NEXT: vaddss ([[BASE]]), [[OUT_Real]], [[RES_Real:%xmm[0-9]+]]
+; Swap Imm and Real.
+; REGULAR-NEXT: vinsertps $16, [[RES_Imm]], [[RES_Real]], [[RES_Vec:%xmm[0-9]+]]
+; Put the results back into out[out_start].
+; REGULAR-NEXT: vmovq [[RES_Vec]], ([[BASE]])
+define void @t1(%class.Complex* nocapture %out, i64 %out_start) {
+entry:
+  %arrayidx = getelementptr inbounds %class.Complex* %out, i64 %out_start
+  %tmp = bitcast %class.Complex* %arrayidx to i64*
+  %tmp1 = load i64* %tmp, align 8
+  %t0.sroa.0.0.extract.trunc = trunc i64 %tmp1 to i32
+  %tmp2 = bitcast i32 %t0.sroa.0.0.extract.trunc to float
+  %t0.sroa.2.0.extract.shift = lshr i64 %tmp1, 32
+  %t0.sroa.2.0.extract.trunc = trunc i64 %t0.sroa.2.0.extract.shift to i32
+  %tmp3 = bitcast i32 %t0.sroa.2.0.extract.trunc to float
+  %add = add i64 %out_start, 8
+  %arrayidx2 = getelementptr inbounds %class.Complex* %out, i64 %add
+  %i.i = getelementptr inbounds %class.Complex* %arrayidx2, i64 0, i32 0
+  %tmp4 = load float* %i.i, align 4
+  %add.i = fadd float %tmp4, %tmp2
+  %retval.sroa.0.0.vec.insert.i = insertelement <2 x float> undef, float %add.i, i32 0
+  %r.i = getelementptr inbounds %class.Complex* %arrayidx2, i64 0, i32 1
+  %tmp5 = load float* %r.i, align 4
+  %add5.i = fadd float %tmp5, %tmp3
+  %retval.sroa.0.4.vec.insert.i = insertelement <2 x float> %retval.sroa.0.0.vec.insert.i, float %add5.i, i32 1
+  %ref.tmp.sroa.0.0.cast = bitcast %class.Complex* %arrayidx to <2 x float>*
+  store <2 x float> %retval.sroa.0.4.vec.insert.i, <2 x float>* %ref.tmp.sroa.0.0.cast, align 4
+  ret void
+}
+
+; Function Attrs: nounwind
+declare void @llvm.memcpy.p0i8.p0i8.i64(i8* nocapture, i8* nocapture readonly, i64, i32, i1) #1
+
+; Function Attrs: nounwind
+declare void @llvm.lifetime.start(i64, i8* nocapture)
+
+; Function Attrs: nounwind
+declare void @llvm.lifetime.end(i64, i8* nocapture)
+
+; Check that we do not read outside of the chunk of bits of the original loads.
+;
+; The 64-bits should have been split in one 32-bits and one 16-bits slices.
+; The 16-bits should be zero extended to match the final type.
+;
+; The memory layout is:
+; LSB 0 1 2 3 | 4 5 | 6 7 MSB
+;      Low            High
+; The base address points to 0 and is 8-bytes aligned.
+; Low slice starts at 0 (base) and is 8-bytes aligned.
+; High slice starts at 6 (base + 6-bytes) and is 2-bytes aligned.
+;
+; STRESS-LABEL: t2:
+; STRESS: movzwl 6([[BASE:[^)]+]]), %eax
+; STRESS-NEXT: addl ([[BASE]]), %eax
+; STRESS-NEXT: ret
+;
+; For the REGULAR heuristic, this is not profitable to slice things that are not
+; next to each other in memory. Here we have a hole with bytes #4-5.
+; REGULAR-LABEL: t2:
+; REGULAR: shrq $48
+define i32 @t2(%class.Complex* nocapture %out, i64 %out_start) {
+  %arrayidx = getelementptr inbounds %class.Complex* %out, i64 %out_start
+  %bitcast = bitcast %class.Complex* %arrayidx to i64*
+  %chunk64 = load i64* %bitcast, align 8
+  %slice32_low = trunc i64 %chunk64 to i32
+  %shift48 = lshr i64 %chunk64, 48
+  %slice32_high = trunc i64 %shift48 to i32
+  %res = add i32 %slice32_high, %slice32_low
+  ret i32 %res
+}
+
+; Check that we do not optimize overlapping slices.
+;
+; The 64-bits should NOT have been split in as slices are overlapping.
+; First slice uses bytes numbered 0 to 3.
+; Second slice uses bytes numbered 6 and 7.
+; Third slice uses bytes numbered 4 to 7.
+;
+; STRESS-LABEL: t3:
+; STRESS: shrq $48
+; STRESS: shrq $32
+;
+; REGULAR-LABEL: t3:
+; REGULAR: shrq $48
+; REGULAR: shrq $32
+define i32 @t3(%class.Complex* nocapture %out, i64 %out_start) {
+  %arrayidx = getelementptr inbounds %class.Complex* %out, i64 %out_start
+  %bitcast = bitcast %class.Complex* %arrayidx to i64*
+  %chunk64 = load i64* %bitcast, align 8
+  %slice32_low = trunc i64 %chunk64 to i32
+  %shift48 = lshr i64 %chunk64, 48
+  %slice32_high = trunc i64 %shift48 to i32
+  %shift32 = lshr i64 %chunk64, 32
+  %slice32_lowhigh = trunc i64 %shift32 to i32
+  %tmpres = add i32 %slice32_high, %slice32_low
+  %res = add i32 %slice32_lowhigh, %tmpres
+  ret i32 %res
+}
+