From c8d277f46e1c6337e7175fe70185d3fe975bfaec Mon Sep 17 00:00:00 2001
From: Harmen Stoppels <harmenstoppels@gmail.com>
Date: Tue, 24 Mar 2020 16:33:28 +0100
Subject: [PATCH] Fix generic mul accidental type promotion Int32 -> Int64
 (#35164)

---
 stdlib/LinearAlgebra/src/matmul.jl  | 8 ++++----
 stdlib/LinearAlgebra/test/matmul.jl | 7 +++++++
 2 files changed, 11 insertions(+), 4 deletions(-)

diff --git a/stdlib/LinearAlgebra/src/matmul.jl b/stdlib/LinearAlgebra/src/matmul.jl
index e5c33388a9af03..66242177f2ea6b 100644
--- a/stdlib/LinearAlgebra/src/matmul.jl
+++ b/stdlib/LinearAlgebra/src/matmul.jl
@@ -649,7 +649,7 @@ function generic_matvecmul!(C::AbstractVector{R}, tA, A::AbstractVecOrMat, B::Ab
         for k = 1:mA
             aoffs = (k-1)*Astride
             if mB == 0
-                s = zero(R)
+                s = false
             else
                 s = zero(A[aoffs + 1]*B[1] + A[aoffs + 1]*B[1])
             end
@@ -662,7 +662,7 @@ function generic_matvecmul!(C::AbstractVector{R}, tA, A::AbstractVecOrMat, B::Ab
         for k = 1:mA
             aoffs = (k-1)*Astride
             if mB == 0
-                s = zero(R)
+                s = false
             else
                 s = zero(A[aoffs + 1]*B[1] + A[aoffs + 1]*B[1])
             end
@@ -676,14 +676,14 @@ function generic_matvecmul!(C::AbstractVector{R}, tA, A::AbstractVecOrMat, B::Ab
             if !iszero(_add.beta)
                 C[i] *= _add.beta
             elseif mB == 0
-                C[i] = zero(R)
+                C[i] = false
             else
                 C[i] = zero(A[i]*B[1] + A[i]*B[1])
             end
         end
         for k = 1:mB
             aoffs = (k-1)*Astride
-            b = _add(B[k], 0)
+            b = _add(B[k], false)
             for i = 1:mA
                 C[i] += A[aoffs + i] * b
             end
diff --git a/stdlib/LinearAlgebra/test/matmul.jl b/stdlib/LinearAlgebra/test/matmul.jl
index 587dc66e4e6a92..a607604e56cc78 100644
--- a/stdlib/LinearAlgebra/test/matmul.jl
+++ b/stdlib/LinearAlgebra/test/matmul.jl
@@ -394,6 +394,13 @@ end
     end
 end
 
+@testset "#35163" begin
+    # typemax(Int32) * Int32(1) + Int32(1) * Int32(1) should wrap around
+    # not promote to Int64, convert to Int32 and throw inexacterror
+    val = mul!(Int32[1], fill(typemax(Int32), 1, 1), Int32[1], Int32(1), Int32(1))
+    @test val[1] == typemin(Int32)
+end
+
 # Number types that lack conversion to the destination type
 struct RootInt
     i::Int