[PowerPC] Fix address-offset folding for plain addi

When folding an addi into a memory access that can take an immediate offset, we
were implicitly assuming that the existing offset was zero. This was incorrect.
If we're dealing with an addi with a plain constant, we can add it to the
existing offset (assuming that doesn't overflow the immediate, etc.), but if we
have anything else (i.e. something that will become a relocation expression),
we'll go back to requiring the existing immediate offset to be zero (because we
don't know what the requirements on that relocation expression might be - e.g.
maybe it is paired with some addis in some relevant way).

On the other hand, when dealing with a plain addi with a regular constant
immediate, the alignment restrictions (from the TOC base pointer, etc.) are
irrelevant.

I've added the test case from PR30280, which demonstrated the bug, but also
demonstrates a missed optimization opportunity (i.e. we don't need the memory
accesses at all).

Fixes PR30280.

llvm-svn: 280789

1 files changed, 40 insertions, 0 deletions

diff --git a/llvm/test/CodeGen/PowerPC/addi-offset-fold.ll b/llvm/test/CodeGen/PowerPC/addi-offset-fold.ll
new file mode 100644
index 00000000000..063bfdb0d47
--- /dev/null
+++ b/llvm/test/CodeGen/PowerPC/addi-offset-fold.ll
@@ -0,0 +1,40 @@
+; RUN: llc < %s | FileCheck %s
+target datalayout = "e-m:e-i64:64-n32:64"
+target triple = "powerpc64le-unknown-linux-gnu"
+
+%struct.S0 = type <{ i32, [5 x i8] }>
+
+; Function Attrs: norecurse nounwind readnone
+define signext i32 @foo([2 x i64] %a.coerce) local_unnamed_addr #0 {
+entry:
+  %a = alloca %struct.S0, align 8
+  %a.coerce.fca.0.extract = extractvalue [2 x i64] %a.coerce, 0
+  %a.coerce.fca.1.extract = extractvalue [2 x i64] %a.coerce, 1
+  %a.0.a.0..sroa_cast = bitcast %struct.S0* %a to i64*
+  store i64 %a.coerce.fca.0.extract, i64* %a.0.a.0..sroa_cast, align 8
+  %tmp.sroa.2.0.extract.trunc = trunc i64 %a.coerce.fca.1.extract to i8
+  %a.8.a.8..sroa_idx = getelementptr inbounds %struct.S0, %struct.S0* %a, i64 0, i32 1, i64 4
+  store i8 %tmp.sroa.2.0.extract.trunc, i8* %a.8.a.8..sroa_idx, align 8
+  %a.4.a.4..sroa_idx = getelementptr inbounds %struct.S0, %struct.S0* %a, i64 0, i32 1
+  %a.4.a.4..sroa_cast = bitcast [5 x i8]* %a.4.a.4..sroa_idx to i40*
+  %a.4.a.4.bf.load = load i40, i40* %a.4.a.4..sroa_cast, align 4
+  %bf.lshr = lshr i40 %a.4.a.4.bf.load, 31
+  %bf.lshr.tr = trunc i40 %bf.lshr to i32
+  %bf.cast = and i32 %bf.lshr.tr, 127
+  ret i32 %bf.cast
+
+; CHECK-LABEL: @foo
+; FIXME: We don't need to do these stores/loads at all.
+; CHECK-DAG: std 3, -24(1)
+; CHECK-DAG: stb 4, -16(1)
+; CHECK: ori 2, 2, 0
+; CHECK-DAG: lbz [[REG1:[0-9]+]], -16(1)
+; CHECK-DAG: lwz [[REG2:[0-9]+]], -20(1)
+; CHECK-DAG: sldi [[REG3:[0-9]+]], [[REG1]], 32
+; CHECK-DAG: or [[REG4:[0-9]+]], [[REG2]], [[REG3]]
+; CHECK: rldicl 3, [[REG4]], 33, 57
+; CHECK: blr
+}
+
+attributes #0 = { nounwind "no-frame-pointer-elim"="true" "no-frame-pointer-elim-non-leaf" "target-cpu"="ppc64le" }
+