[llvm] f98ed74 - [LSR] Handle case 1*reg => reg. PR50918

[Max Kazantsev via llvm-commits]

Author: Max Kazantsev
Date: 2021-07-16T11:33:59+07:00
New Revision: f98ed74f6910f8b09e77497aeb30c860c433610d

URL: https://github.com/llvm/llvm-project/commit/f98ed74f6910f8b09e77497aeb30c860c433610d
DIFF: https://github.com/llvm/llvm-project/commit/f98ed74f6910f8b09e77497aeb30c860c433610d.diff

LOG: [LSR] Handle case 1*reg => reg. PR50918

This patch addresses assertion failure in case when the only found formula for LSR
is `1*reg => reg` which was supposed to be an impossible situation, however there
is a test that shows it is possible.

In this case, we can use scale register with scale of 1 as the missing base register.

Reviewed By: huihuiz, reames
Differential Revision: https://reviews.llvm.org/D105009

Added: 
    llvm/test/Transforms/LoopStrengthReduce/pr50918.ll

Modified: 
    llvm/lib/Transforms/Scalar/LoopStrengthReduce.cpp

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Transforms/Scalar/LoopStrengthReduce.cpp b/llvm/lib/Transforms/Scalar/LoopStrengthReduce.cpp
index acf741d270fea..548874606292f 100644
--- a/llvm/lib/Transforms/Scalar/LoopStrengthReduce.cpp
+++ b/llvm/lib/Transforms/Scalar/LoopStrengthReduce.cpp
@@ -511,9 +511,16 @@ bool Formula::isCanonical(const Loop &L) const {
 void Formula::canonicalize(const Loop &L) {
   if (isCanonical(L))
     return;
-  // So far we did not need this case. This is easy to implement but it is
-  // useless to maintain dead code. Beside it could hurt compile time.
-  assert(!BaseRegs.empty() && "1*reg => reg, should not be needed.");
+
+  if (BaseRegs.empty()) {
+    // No base reg? Use scale reg with scale = 1 as such.
+    assert(ScaledReg && "Expected 1*reg => reg");
+    assert(Scale == 1 && "Expected 1*reg => reg");
+    BaseRegs.push_back(ScaledReg);
+    Scale = 0;
+    ScaledReg = nullptr;
+    return;
+  }
 
   // Keep the invariant sum in BaseRegs and one of the variant sum in ScaledReg.
   if (!ScaledReg) {

diff  --git a/llvm/test/Transforms/LoopStrengthReduce/pr50918.ll b/llvm/test/Transforms/LoopStrengthReduce/pr50918.ll
new file mode 100644
index 0000000000000..fdb93c298b76d
--- /dev/null
+++ b/llvm/test/Transforms/LoopStrengthReduce/pr50918.ll
@@ -0,0 +1,41 @@
+; RUN: opt -S -loop-reduce < %s | FileCheck %s
+;
+; Make sure we don't fail an assertion here.
+
+target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128-ni:1-p2:32:8:8:32-ni:2"
+target triple = "x86_64-unknown-linux-gnu"
+
+define void @test() {
+; CHECK-LABEL: test
+bb:
+  br label %bb1
+
+bb1:                                              ; preds = %bb12, %bb
+  %tmp2 = phi i64 [ 94, %bb ], [ %tmp20, %bb12 ]
+  %tmp3 = phi i32 [ -28407, %bb ], [ %tmp23, %bb12 ]
+  %tmp4 = trunc i64 %tmp2 to i32
+  %tmp5 = add i32 %tmp3, %tmp4
+  %tmp6 = mul i32 undef, %tmp5
+  %tmp7 = sub i32 %tmp6, %tmp5
+  %tmp8 = shl i32 %tmp7, 1
+  %tmp9 = add i32 %tmp8, %tmp3
+  %tmp10 = add i32 %tmp9, %tmp4
+  %tmp11 = shl i32 %tmp10, 1
+  br label %bb21
+
+bb12:                                             ; preds = %bb21
+  %tmp13 = mul i32 %tmp22, -101
+  %tmp14 = add i32 %tmp22, 2
+  %tmp15 = add i32 %tmp14, %tmp13
+  %tmp16 = trunc i32 %tmp15 to i8
+  %tmp17 = shl i8 %tmp16, 5
+  %tmp18 = add i8 %tmp17, 64
+  %tmp19 = sext i8 %tmp18 to i32
+  %tmp20 = add nsw i64 %tmp2, -3
+  br label %bb1
+
+bb21:                                             ; preds = %bb21, %bb1
+  %tmp22 = phi i32 [ %tmp11, %bb1 ], [ %tmp23, %bb21 ]
+  %tmp23 = add i32 %tmp22, 1
+  br i1 false, label %bb12, label %bb21
+}