[ARM] Parallel DSP Pass

Armv6 introduced instructions to perform 32-bit SIMD operations. The purpose of
this pass is to do some straightforward IR pattern matching to create ACLE DSP
intrinsics, which map on these 32-bit SIMD operations.

Currently, only the SMLAD instruction gets recognised. This instruction
performs two multiplications with 16-bit operands, and stores the result in an
accumulator. We will follow this up with patches to recognise SMLAD in more
cases, and also to generate other DSP instructions (like e.g. SADD16).

Patch by: Sam Parker and Sjoerd Meijer

Differential Revision: https://reviews.llvm.org/D48128

llvm-svn: 335850

1 files changed, 53 insertions, 0 deletions

diff --git a/llvm/test/CodeGen/ARM/smlad7.ll b/llvm/test/CodeGen/ARM/smlad7.ll
new file mode 100644
index 00000000000..b8e54e6e223
--- /dev/null
+++ b/llvm/test/CodeGen/ARM/smlad7.ll
@@ -0,0 +1,53 @@
+; RUN: opt -mtriple=arm-arm-eabi -mcpu=cortex-m33 < %s -parallel-dsp -S | FileCheck %s
+;
+; Alias check: check that the rewrite isn't triggered when there's a store
+; aliasing one of the mul load operands. Arguments are now annotated with
+; 'noalias'.
+;
+; CHECK-NOT:  call i32 @llvm.arm.smlad
+;
+define dso_local i32 @test(i32 %arg, i32* noalias %arg1, i16* noalias readonly %arg2, i16* noalias readonly %arg3) {
+entry:
+  %cmp24 = icmp sgt i32 %arg, 0
+  br i1 %cmp24, label %for.body.preheader, label %for.cond.cleanup
+
+for.body.preheader:
+  %.pre = load i16, i16* %arg3, align 2
+  %.pre27 = load i16, i16* %arg2, align 2
+  br label %for.body
+
+for.cond.cleanup:
+  %mac1.0.lcssa = phi i32 [ 0, %entry ], [ %add11, %for.body ]
+  ret i32 %mac1.0.lcssa
+
+for.body:
+  %mac1.026 = phi i32 [ %add11, %for.body ], [ 0, %for.body.preheader ]
+  %i.025 = phi i32 [ %add, %for.body ], [ 0, %for.body.preheader ]
+  %arrayidx = getelementptr inbounds i16, i16* %arg3, i32 %i.025
+  %0 = load i16, i16* %arrayidx, align 2
+
+; Store inserted here, aliasing only with loads from 'arrayidx'.
+  store i16 42, i16* %arrayidx, align 2
+
+  %add = add nuw nsw i32 %i.025, 1
+  %arrayidx1 = getelementptr inbounds i16, i16* %arg3, i32 %add
+  %1 = load i16, i16* %arrayidx1, align 2
+  %arrayidx3 = getelementptr inbounds i16, i16* %arg2, i32 %i.025
+  %2 = load i16, i16* %arrayidx3, align 2
+  %conv = sext i16 %2 to i32
+  %conv4 = sext i16 %0 to i32
+  %mul = mul nsw i32 %conv, %conv4
+  %arrayidx6 = getelementptr inbounds i16, i16* %arg2, i32 %add
+  %3 = load i16, i16* %arrayidx6, align 2
+  %conv7 = sext i16 %3 to i32
+  %conv8 = sext i16 %1 to i32
+  %mul9 = mul nsw i32 %conv7, %conv8
+  %add10 = add i32 %mul, %mac1.026
+
+; Here the Mul is the LHS, and the Add the RHS.
+  %add11 = add i32 %mul9, %add10
+
+  %exitcond = icmp ne i32 %add, %arg
+  br i1 %exitcond, label %for.body, label %for.cond.cleanup
+}
+