[LSR] Don't allow zero quotient as scale ref. PR56160

Scale reg should never be zero, so when the quotient is zero, we
cannot assign it there. Limit this transform to avoid this situation.

Differential Revision: https://reviews.llvm.org/D128339
Reviewed By: eopXD

diff --git a/llvm/lib/Transforms/Scalar/LoopStrengthReduce.cpp b/llvm/lib/Transforms/Scalar/LoopStrengthReduce.cpp
index f0a5f94..9959e40 100644 (file)
--- a/llvm/lib/Transforms/Scalar/LoopStrengthReduce.cpp
+++ b/llvm/lib/Transforms/Scalar/LoopStrengthReduce.cpp
@@ -4080,23 +4080,24 @@ void LSRInstance::GenerateScales(LSRUse &LU, unsigned LUIdx, Formula Base) {
           continue;
         // Divide out the factor, ignoring high bits, since we'll be
         // scaling the value back up in the end.
-        if (const SCEV *Quotient = getExactSDiv(AR, FactorS, SE, true)) {
-          // TODO: This could be optimized to avoid all the copying.
-          Formula F = Base;
-          F.ScaledReg = Quotient;
-          F.deleteBaseReg(F.BaseRegs[i]);
-          // The canonical representation of 1*reg is reg, which is already in
-          // Base. In that case, do not try to insert the formula, it will be
-          // rejected anyway.
-          if (F.Scale == 1 && (F.BaseRegs.empty() ||
-                               (AR->getLoop() != L && LU.AllFixupsOutsideLoop)))
-            continue;
-          // If AllFixupsOutsideLoop is true and F.Scale is 1, we may generate
-          // non canonical Formula with ScaledReg's loop not being L.
-          if (F.Scale == 1 && LU.AllFixupsOutsideLoop)
-            F.canonicalize(*L);
-          (void)InsertFormula(LU, LUIdx, F);
-        }
+        if (const SCEV *Quotient = getExactSDiv(AR, FactorS, SE, true))
+          if (!Quotient->isZero()) {
+            // TODO: This could be optimized to avoid all the copying.
+            Formula F = Base;
+            F.ScaledReg = Quotient;
+            F.deleteBaseReg(F.BaseRegs[i]);
+            // The canonical representation of 1*reg is reg, which is already in
+            // Base. In that case, do not try to insert the formula, it will be
+            // rejected anyway.
+            if (F.Scale == 1 && (F.BaseRegs.empty() ||
+                                 (AR->getLoop() != L && LU.AllFixupsOutsideLoop)))
+              continue;
+            // If AllFixupsOutsideLoop is true and F.Scale is 1, we may generate
+            // non canonical Formula with ScaledReg's loop not being L.
+            if (F.Scale == 1 && LU.AllFixupsOutsideLoop)
+              F.canonicalize(*L);
+            (void)InsertFormula(LU, LUIdx, F);
+          }
       }
     }
   }

diff --git a/llvm/test/Transforms/LoopStrengthReduce/pr56160.ll b/llvm/test/Transforms/LoopStrengthReduce/pr56160.ll
new file mode 100644 (file)
index 0000000..1a1b5e4
--- /dev/null
+++ b/llvm/test/Transforms/LoopStrengthReduce/pr56160.ll
@@ -0,0 +1,39 @@
+; RUN: opt -S -loop-reduce %s | FileCheck %s
+
+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"
+
+; Make sure we don't crash.
+define void @test() {
+; CHECK-LABEL: @test(
+bb:
+  %tmp = load atomic i64, i64 addrspace(1)* undef unordered, align 8
+  %tmp1 = sub i64 4294967294, undef
+  br label %bb5
+
+bb2:                                              ; No predecessors!
+  %tmp3 = add i32 undef, %tmp24
+  unreachable
+
+bb5:                                              ; preds = %bb5, %bb
+  %tmp6 = phi i64 [ %tmp18, %bb5 ], [ %tmp, %bb ]
+  %tmp7 = phi i32 [ %tmp19, %bb5 ], [ undef, %bb ]
+  %tmp8 = phi i32 [ %tmp24, %bb5 ], [ undef, %bb ]
+  %tmp9 = sub i32 %tmp8, undef
+  %tmp10 = zext i32 %tmp9 to i64
+  %tmp11 = add i32 %tmp7, 1
+  %tmp12 = zext i32 %tmp11 to i64
+  %tmp13 = add i64 %tmp1, %tmp12
+  %tmp14 = add i64 %tmp6, %tmp10
+  %tmp15 = sub i64 %tmp14, %tmp13
+  %tmp16 = trunc i64 %tmp15 to i32
+  %tmp17 = add i32 undef, %tmp16
+  %tmp18 = add i64 %tmp6, 2
+  %tmp19 = add i32 %tmp7, 2
+  %tmp20 = xor i64 %tmp6, -1
+  %tmp21 = add i64 %tmp1, %tmp20
+  %tmp22 = trunc i64 %tmp21 to i32
+  %tmp23 = add i32 %tmp19, %tmp22
+  %tmp24 = add i32 %tmp17, %tmp23
+  br label %bb5
+}